I went through and made sure every computer had a valid cc_config.xml file including <allow_remote_gui_rpc>1</allow_remote_gui_rpc>. It did not fix any of them. I've continued to look for differences but I can find nothing that helps.
Any other suggestions???

Thanks OldChap, but it didn't fix it. All my computers have static IPs so they don't change. I checked every one for those 3 files and they're all right. I wish Fred did not asterisk-out the password on Computer tab, annoying.
I've also tried removing the computer and using Find Computers.
I have 2 Win7 and 3 Linux 19 computers that are running BOINC just fine but won't communicate with BOINCTasks 1.78.
It's something subtle.

so let's start with cc_config.xml

here is mine that works on all of my rigs. Just so you can totally rule that out

<cc_config> <log_flags> <file_xfer>1</file_xfer> <sched_ops>1</sched_ops> <task>1</task> <android_debug>0</android_debug> <app_msg_receive>0</app_msg_receive> <app_msg_send>0</app_msg_send> <async_file_debug>0</async_file_debug> <benchmark_debug>0</benchmark_debug> <checkpoint_debug>0</checkpoint_debug> <coproc_debug>0</coproc_debug> <cpu_sched>0</cpu_sched> <cpu_sched_debug>0</cpu_sched_debug> <cpu_sched_status>0</cpu_sched_status> <dcf_debug>0</dcf_debug> <disk_usage_debug>0</disk_usage_debug> <file_xfer_debug>0</file_xfer_debug> <gui_rpc_debug>0</gui_rpc_debug> <heartbeat_debug>0</heartbeat_debug> <http_debug>0</http_debug> <http_xfer_debug>0</http_xfer_debug> <idle_detection_debug>0</idle_detection_debug> <mem_usage_debug>0</mem_usage_debug> <network_status_debug>0</network_status_debug> <notice_debug>0</notice_debug> <poll_debug>0</poll_debug> <priority_debug>0</priority_debug> <proxy_debug>0</proxy_debug> <rr_simulation>0</rr_simulation> <rrsim_detail>0</rrsim_detail> <sched_op_debug>0</sched_op_debug> <scrsave_debug>0</scrsave_debug> <slot_debug>0</slot_debug> <state_debug>0</state_debug> <statefile_debug>0</statefile_debug> <suspend_debug>0</suspend_debug> <task_debug>0</task_debug> <time_debug>0</time_debug> <trickle_debug>0</trickle_debug> <unparsed_xml>0</unparsed_xml> <work_fetch_debug>0</work_fetch_debug> </log_flags> <options> <abort_jobs_on_exit>0</abort_jobs_on_exit> <allow_multiple_clients>1</allow_multiple_clients> <allow_remote_gui_rpc>1</allow_remote_gui_rpc> <client_version_check_url>https://boinc.berkeley.edu/download.php?xml=1</client_version_check_url> <client_new_version_text></client_new_version_text> <client_download_url>https://boinc.berkeley.edu/download.php</client_download_url> <disallow_attach>0</disallow_attach> <dont_check_file_sizes>0</dont_check_file_sizes> <dont_contact_ref_site>0</dont_contact_ref_site> <lower_client_priority>0</lower_client_priority> <dont_suspend_nci>0</dont_suspend_nci> <dont_use_vbox>0</dont_use_vbox> <exit_after_finish>0</exit_after_finish> <exit_before_start>0</exit_before_start> <exit_when_idle>0</exit_when_idle> <fetch_minimal_work>0</fetch_minimal_work> <fetch_on_update>0</fetch_on_update> <force_auth>default</force_auth> <http_1_0>0</http_1_0> <http_transfer_timeout>300</http_transfer_timeout> <http_transfer_timeout_bps>10</http_transfer_timeout_bps> <max_event_log_lines>2000</max_event_log_lines> <max_file_xfers>8</max_file_xfers> <max_file_xfers_per_project>8</max_file_xfers_per_project> <max_stderr_file_size>0</max_stderr_file_size> <max_stdout_file_size>0</max_stdout_file_size> <max_tasks_reported>0</max_tasks_reported> <ncpus>32</ncpus> <network_test_url>https://www.google.com/</network_test_url> <no_alt_platform>0</no_alt_platform> <no_gpus>0</no_gpus> <no_info_fetch>0</no_info_fetch> <no_opencl>0</no_opencl> <no_priority_change>1</no_priority_change> <os_random_only>0</os_random_only> <process_priority>-1</process_priority> <process_priority_special>-1</process_priority_special> <proxy_info> <socks_server_name></socks_server_name> <socks_server_port>80</socks_server_port> <http_server_name></http_server_name> <http_server_port>80</http_server_port> <socks5_user_name></socks5_user_name> <socks5_user_passwd></socks5_user_passwd> <http_user_name></http_user_name> <http_user_passwd></http_user_passwd> <no_proxy></no_proxy> </proxy_info> <rec_half_life_days>10.000000</rec_half_life_days> <report_results_immediately>0</report_results_immediately> <run_apps_manually>0</run_apps_manually> <save_stats_days>30</save_stats_days> <skip_cpu_benchmarks>0</skip_cpu_benchmarks> <simple_gui_only>0</simple_gui_only> <start_delay>0.000000</start_delay> <stderr_head>0</stderr_head> <suppress_net_info>0</suppress_net_info> <unsigned_apps_ok>0</unsigned_apps_ok> <use_all_gpus>1</use_all_gpus> <use_certs>0</use_certs> <use_certs_only>0</use_certs_only> <vbox_window>0</vbox_window> </options> </cc_config>

OldChap, Comparing your cc_config.xml to mine line by line. I used Wiki https://boinc.berkeley.edu/wiki/Client_configuration as my definitions.
<log_flags> <!-- disabled by default anyway -->
<android_debug>0</android_debug> <!-- This option not found in the Wiki -->
</log_flags>
<options>
<allow_multiple_clients>1</allow_multiple_clients> <!-- 0, I don't allow this, no need -->
<dont_use_vbox>0</dont_use_vbox> <!-- I use 1 since I don't use VB. -->
<dont_suspend_nci>0</dont_suspend_nci> <!-- You use 0 I use 1. Wiki is worded ambiguously so I don't know what this means. "If set {to 1?}, exempt non-CPU-intensive tasks from suspension in most cases." -->
<fetch_on_update>0</fetch_on_update> <!-- I use 1 -->
<force_auth>default</force_auth> <!-- I deleted this since I don't use a proxy server. "When authenticating against a proxy server use a specific authentication method. Valid parameters are: basic, digest, gss-negotiate, ntlm (Setting of particular importance for World Community Grid to facilitate SSL/HTTPS communications)" -->
<max_file_xfers>8</max_file_xfers> <!-- I use 32 for both of these. Works great for DLing but FCC throttles UL speed. -->
<max_file_xfers_per_project>8</max_file_xfers_per_project>
<ncpus>32</ncpus> <!-- This one is nice. Change it & click Options/Read config files & watch it change. If only using BOINC I use -1. If I'm running Folding@Home I set this to #CPUs - #GPUs -->
<rec_half_life_days>10.000000</rec_half_life_days> <!-- I use 7 to be more responsive. Helped during summer with TOU electric rates. -->
<save_stats_days>30</save_stats_days> <!-- I use 1000. I like graphs. I still like graphs. I really like graphs. -->
</options>