[SOLVED] Type Mismatch 13 - setting worksheet to another worksheet not working

Dear forum members,

I receive a runtime error 13 (type mismatch) when I try to set a worksheet to another worksheet; the code

 Set From_Sheet_SDE = Filename_FROM.Worksheets("SDE")

gets highlighted. I am a novice when it comes to VBA; I have coded quite a bit of MATLAB and Python though, so I have an understanding for algorithm theory.
Your help in finding why Excel thinks the two worksheets are incompatible is highly appreciated.

The code in its entirity is a bit too long for this thread; I have attached it as a file instead.