Do you have any add-ins loaded? If so, it is probably an add-in
misbehaving. Go in to the VBA Editor, and for each project listed
in the Project Explorer (CTRL+R to view it), go to the Tools menu
and choose References. See if any are marked MISSING. If so,
uncheck them.

Signature
Cordially,
Chip Pearson
Microsoft MVP - Excel
Pearson Software Consulting, LLC
www.cpearson.com
> Seemingly all of a sudden I get the message User-Defined Type
> Not Defined
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>
> How can I stop this from happening? Thank you.