BOINC keeps track of valid tasks.

When a new application is introduced for every host the number is 5, I think it was.
This value is raised with every valid task returned and reduced with each error task.
When it's zero, that host will not get new tasks that day.

I had this problem on Einstein@Home and was advised to create a profile I wasn't using (ie HOME, SCHOOL, or WORK) and minimize its settings, then assign any erroring computers to that profile..

@tonyh205, thank you for the links and background information. I'm glad I'm not the only one who thought it was annoying. :)

It looks like seippel did some research on the overall error rates, which when put to scale, I'm sure it's very, very low, but I can't help but question if this is a farm of computers at the same company or university where they were installed en masse and simply abandoned or otherwise a service account got "stripped" which would prevent BOINC from getting the privileges it needs to run as a Windows service. Maybe an employee quit the company, etc.

Continuing to give these mischievous machines more WUs day after day is just asking for punishment. Isn't the definition of insanity trying the same thing over and over and expecting different results? :P

I realize this is bringing up just a sore subject, but it's ineffiicient to the overall project, and I wish there was more "control" over cutting these machines off the project until they are remedied instead of constantly forgiving them as if they'll suddenly stop erroring! Windows Enterprise licenses are strictly for corporate or university/academic use, so this has to be a whole group of machines that have been neglected.