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.
When you set up Shift appearance and format on the Data sets tab of the DCS (see pic1), you tell DCS how to show the Shift field. But you never actually show this field in the report, so these settings are never applied.
The fields you actually show are Shift.Start.DateParts.MonthName and Shift.Start.DateParts.Year (see pic2) and they do what you need, but you told DCS to show them in two different columns, which is exactly what it did (see pic3).
I suggest, you remove all formatting from the Shift field on the Data set tab and show Shift.Start.BeginDates.BegOfMonth instead of Shift.Start.DateParts.MonthName and Shift.Start.DateParts.Year on the Settings tab.
Then you can use Conditional appearance setting to format the Shift.Start.BeginDates.BegOfMonth field (see pic4). The trick here is not to specify any condition, so the report always apply this format to this field.
In the format setting you should use the format expression, you've already found: DF='MMMM yyyy'
This was NOT an exam. We just used some of the exam tasks to help you learn the platform, that's all. Exam is passed in a very different way: you will have limited time (6 hours) and you won't be able to consult anyone until the end of the certification.
You are welcome to apply for the formal exam, and you will get your certification as soon as you pass it.