Opening new mail in Outlook causes Excel to close!

[ojhand]

Hi,
very weird issue that I'm having: I open an excel attachment, copy
data to my clipboard, then switch back to outlook to open a new mail
message - excel then closes down (including any other spreadsheets
that may be open other than the attached one) and the data I've copied
isn't on the clipboard any more.
Any hints and tips much appreciated
Thanks!