I attempted to edit your UserForm from the download in Post #6 (Look on right side of posting headers above for #'s). I receive an error message saying I don't have permission to make changes. Looking over your workbook however, I do not find any setting or syntax coding that would prevent me from making edits. I then added a new UserForm (#2) and received the same error message. I mention this because of it being unusual ... no indication the form is protected, that I can find.

Two questions: Will the data in columns K & L always remain static ? Are you using those entries like a small database of selections from which to choose and the info will never change ? Or at some point, will you be changing your inventory of materials, dimensions, etc ?

Secondly, (your answer to the first question may answer this one), what is the purpose of "copying" the data from columns K & L via the combobox's then pasting same in the first few columns ?
If the answer to my first question is 'YES', it may work more efficiently for you to code your data as indicated in my post #2. This approach may also clear up your issue with first selection of the combobox.