Summary
If you get the following error message: "Overflow while converting variant of type (Double) into type (integer)" when running iX Plan
In-Depth
This is because the "Decimal symbol" setting in Windows regional settings has to be a dot "." and nothing else.
Right click the start menu - Settings - Time & Language - Date, time & regional formatting - Additional date, time & regional settings - Change date, time, or number formats - Additional settings - Decimal symbol