Tricky problem, and I don't have any answers.

I know for a fact that a single SNMP set request can have multiple varbinds, I've done this when configuring ATM circuits using Cisco WAN Manager using Net::SNMP for years.

One question is what version of SNMP are you using? I'm suspecting v3 because of the authentication malarkey..

Article SNMP Error using Net::SNMP - Transport endpoint is not connected doesn't appear to shed any light on the problem. For the most part SNMP is UDP, however I suspect v3 (because of security and encryption) could use TCP (in which case being connected to a Transport Endpoint actually has some meaning).

Hunting through the internet I found Re: Samba, Howto eliminate the getpeername failed error message, which could have some meaning if you are using Windows XP. Looking through the source of Net::SNMP I could find no reference to the error message "Transport endpoint is not connected" so I'm guessing it is a system error related to the getpeername() function.