Impossible to find the problem with Month starting with Monday

As it is difficult for me to explain, check directly the attached file.
The macro is made to manage different shift in a team.
On the start Tab, the button "Calendar" allows to create a month calendar (the other button only allows to change shifts).

All is working perfectly ... until you choose a month starting on a Monday (e.g. 10.2012 or 04.2013).

The problem is surely coming from the following part of the part of the macro:

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This allows me to compare the first day of the month and use it to start the table.
Apparently, it does not like when using Monday the first ...

I thought about using a "If, else" to match MyStr3 with the cell in the table, and directly select one cell (would only be 7 lines of control), but it does not work either (not at all this time !!!).

I would really appreciate some help. I have spent 2 days on it, and get crazy !!!