I have written a C# code in console application to open two excels and copy and paste data from one excel to another excel. It was working fine until the destination excel\'
Ran into this problem on my machine. Excel is fully activated and already the default program for .xlsx files. I was loading a workbook template I created with pivot tables and having a script update the data in the tables. Turns out that if the pivot tables are set to "Refresh data when opening the file" under Pivot Table Options > Data, it causes some sort of threading contention issues.
Disabling the refresh on opening solved the issue.