Custom SNMP query returns "nan" on alcatel switch

[Happiness0]

Hi

I'm new to cacti. I try to use the "SNMP - Generic OID" template to get datas from an Alcatel OmniStack LS 6200 switch. According to the wiki, i added the device and used the "new graph" menu, entered the OID i want.
If i use snmpwalk, i get the informations, and the rrd file is created, but it contain only "nan" values.
Sorry for my bad english, not my native language.

[Happiness0]

Here is a dump of the rrd file i'm using. I have cuted some rows on the database, but only "nan" values

[Soup]

What information are you trying to get from the switch?

[Happiness0]

I am trying to get the status of the switch's ports. I am using the OID i've found with the "snmpwalk" command : 1.3.6.1.2.1.2.2.1.8.x. I also tried IF-MIB::ifOperStatus.1 as OID. Not worked.
My final goal is to get datas like errors, bandwidth from each port.

[EDIT] Cacti log file returning "CMDPHP: Poller[0] Host[8] DS[32] WARNING: Result from SNMP not valid. Partial Result: U "