The crashing was caused by exessive 'Exit For' in my code. I divided my script into separate blocks to lessen the amount of nestings - so now I have better overview of them!
Also I now open the every source file I read the data from in a separate instance, and close it after the data are read and processed. Like:
Code:
...
Dim oInst As Object
...
For strSourceNameRow = 1 To NumberOfSourceFiles
strSourceFile = <full path for source file to be opened>
Set oInst = GetObject(strSourceFile)
...
GoTo ExitSourceNameRow
...
ExitSourceNameRow:
' Activate the converter file, and Close the source file
Workbooks(strSourceFileName).Activate
Workbooks(strSourceFileName).Close savechanges:=False
oInst.Close
Set oInst = Nothing
Workbooks(strThisFile).Activate
...