The last two characters of the name are .5, that seems to be causing your problem. Excel is interpreting the .5 as a file extension so is not adding .xlsx.
Change your formula to =CONCATENATE(F33," ",S25," ",F18,F20,M22," ","PR"," ",P7&".xlsx") and the code works.
If you want to save then macros then use
=CONCATENATE(F33," ",S25," ",F18,F20,M22," ","PR"," ",P7&".xlsm")
Also change the 51 in this line of code to 52