An error has been discovered in the excel sheet regarding compensatory time off (avspasering) in April, which causes the time to be added instead of deducted.

 This is easily corrected by doing the following:

Go to line 168 in the form, highlight cell 168 E.  In the formula box you will see that it says:  =SUMMER(E137:E167)-H168.
The minus sign should be +, so replace the text with the following: =SUMMER(E137:E167)+H168