That particular variant of the 3750E (DC power version) is not a supported product according to the compatibility guide. (Reference)
The sysObjectID that LMS is expecting for the closely related devices (Cisco Catalyst 3750E-24TD-E,S)
is 1.3.6.1.4.1.9.1.789. You can use snmpwalk to confirm if your switch returns that OID.
If not, I would suggest opening a TAC case to see if they would accept an enhancement request (ER) for adding the switch. It's end-of-sales but it doesn't hurt to ask.