Template:FAQ:MIBs 10
From Net-SNMP Wiki
Any MIB file starts with an (optional) list of identifiers that it "imports" from other files. The parser handles this using a fixed size buffer to hold the import information. There are two circumstances in which this can result in the error message shown above.
Firstly, if the MIB file refers to an unusually large number of external identifiers. Handling this case requires a (trivial) patch to the parsing code. Contact the coders list for advice. (This is extremely rare - the only example that we've come across is the Cabletron Trap MIB).
Much more common is a syntax error in the IMPORTS clause of the MIB file in question. In particular, check that this section ends in a semicolon, before going on to the main MIB object definitions.