pg_dump problem

Hi,

After doing a pg_dump on a database I'm unable to access the file.

My command is simply 'mv' ::

mv camper.dump20020116 camper_bak/

The error I get is ::

mv: camper.dump20020116: Value too large for defined data type

Strange. It seems to be saying the file I created is too large to handle.
Do you know where I've gone wrong ?
I just want to dump one of my databases, move it to a back up dir. then 
make changes to the running database.

Thank you kindly
Regards
Rudi Starcevic