Custom Number Format

Sent this already but for some reason when I click onto the message board item I get the text of someone elses query.

My problem is that I want to change the number format of a cell to +0.0%;[red]-0.0%.

While I've done this many times in the past I am now getting a message 'no new formats can be added'

I am also unable to paintbrush copy and paste the format from another document - all that happens is that the cell goes to 0.00000 format.

Presumably there is a custom format file somewhere that is 'full' but I can't find any way to locate it and
It also puzzles me that ever time I create a new worksheet previous custom changes made on other documents don't get copied over into the custom format list.

Any suggestions? I am using Excel97.

I am using Excel97