Akos,
Good luck. I have a ticket open on this issue for several days now with no answers. I set snmp properties under administration and via edit on the individual device but after awhile it always goes back to 2 retries and 1 sec. This causes numerous problems when trying to manage the devices. Some devices cannot obtain the inventory or configuration and become managed with warnings or worse unmanaged.
If you want my opinion Prime Infrastructure is a beta (maybe even an alpha) product. There are too many bugs for this product to have gone live. And yes I am running the latest and "greatest" code. I hate to include in my rant opening a ticket on PI. It doesn't exist as a category when opening a ticket. You have to open the ticket under CW Prime and then get transferred to the correct group. Your best bet is creating a ticket using the 800 number. Lastly getting the correct entitlement on your account. I purchased CWLMS and upgraded to CW Prime LMS and received my free entitlement to PI via the PUT. BUT I cannot access any new files because I get the "Additional Entitlement Required" when trying to download patches. My SE has been working to correct this problem for months with no luck.
Again I'm sorry to rant but this snmp issue was the straw that broke the camels back!