Find and remove User Defined Functions

[Moosles]

I am updating an old workbook which was created years ago, and when sending to others for their review they are getting the following message:

There used to be a User Defined Function in a VBA module but I deleted this as it was not needed. I can't seem to find the isformula User Defined Function anywhere else in the workbook, but I'd like to be able to delete it so that this error message goes away, how would I do this? The function is used nowhere in the file and is not referenced anywhere else in the VBA, but I'd like to get rid of this message - any ideas?

 

[Alex Blakenburg]

If you go into a cell and type =isfor you should get a drop down list of suggestions. Do you get 1 or 2 isformulas in the drop down box ?
If you get 2 then there is a function kicking around in there somewhere.
1) In the VBA project window try Ctrl+F enter isformula in the search box. Tick the In Project box and hit enter.
If you don't find anything
2) Disable any Add-Ins that you might have enabled and see if that fixes it.