The error you're seeing has nothing to do with Task2. This is Task1 that does not pass the check. The Task1 report cannot even be opened now because of the error in your source code. Please, get back to Task1 and fix the issue.
You set up the ShiftSchedule periodicity to Monthly. Because of this setting the register requires month to be set when you add a new record. And it's not how you build this report anyway. You shouldn't change any settings of the register.
Please, restore the original register settings and start the report over.
Mesut, you didn't do what I showed you. Let me explain one more time. The Columns setting (see ShiftStart screenshot) tells the report what data you want to group into each column. You set the column to Shift.Start. Each shift starts at a different time. Therefore, only one shift will go into each column. Therefore, you will have as many columns as shifts.
You had to set Columns to the beginning of month (see the BegOfMonth screenshot). This way several shifts will go into the same column because they start in the same month. This will give you the result you need.