Cannot insert object - macro button

[Kevryl]

I have a large file under Excel 2000 and every time I try to insert another
macro button from the toolbox menu I get a response "cannot insert object".
It doesn't tell me why, just that it can't. I can copy another one and change
the macro the copy refers to, but I can't insert a new button. Copying is a
clumsy work around, and thats OK, but I wonder whether this file - a vital
one in my business - is starting to become unstable in some way and why. Oh,
protection is off.

Thanks Keith