Jeffrey,
Thanks but problem arises when I use the Callout tool. If I understand Mike correctly the error message is telling me that the word 'callout' is somewhere in that drawing file so I need to rename it, but I cannot find anything with that name.
The problem may be because I exported the file as a dwg, emailed it to a ACAD colleague who emailed it back (as a dwg) with some work added. It was then that the problem arose. Even by deleting all of the classes (except none and dimension) the callout tool would still not work!
TW