Help please - IIgs Error 0911

[psyc285@csc.canterbury.ac.nz]

I seem to get a relatively frequent fatal system error - 0911
This happens whenever I copy a large number of files - a directory of
150 files is almost always a sure thing - and sometimes when playing
some games - such as 'Out of this World' and 'Shanghai'.

Can anyone give my a clue as to possible causes ( I have looked up the
manual, and ADB Sync Error doesn't make much sense when I am sitting
watching files being copied.)

Config:
Apple IIgs  ROM 1
8 Mb
Ramfast   230Mb HD
8MHz  Zip

Thanks for any help