ArcMain IOMODULE error "DataConnector will not be able to determine the RECORD length."

Tools & Utilities
m1b
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ArcMain IOMODULE error "DataConnector will not be able to determine the RECORD length."

Hi,

I have a module written in C, compiled as a shard object, passed to ArcMain via IOMODULE. It runs fine in a 32 bit environment with 32 bit arcmain, but when I run it with the 64 bit arcmain on a 64 bit environment, compiled specifically with 64 bit switches, it gives me this error:

*** Failure ARC0805:Access Module returned error code 2:

                     Bad parameter passed to Access Module API !ERROR!

                     DataConnector will not be able to determine the RECORD

                     length. Minimum block size for FASTLOAD and BINARY

                     dataformat is 2.

Any idea what does this error mean, where I may be able to start looking for a resolution to it? 

Many thanks in advance

/mb