No problem...

another tip....

You can enter actual dates in row 2, and format the cells to appear as you desire... so after entering a real date, format cells, custom: ddd dd.mm

Then the formula would be changed too:

=SUMIF(INDIRECT("'"&TEXT(B$2,"ddd dd.mm")&"'!C3:C275"),$A4,INDIRECT("'"&TEXT(B$2,"ddd dd.mm")&"'!F3:F275"))

still need consistency in tab names....