Hi Christian,
My resolution is 2.1 Ang.. So its high enough for individual B-Factor refinement. The density for this particular atom is not that good, which explains the high B-Factor for this. As the other atoms of the ligand have reasonble B-Factors compared to the main chain they seems to be nearly fully occupied. I am a bit in doubt about the possibilty that between the two connected atoms the B-Factor changes so drastically. The R-Factors are absolutely O.K R/Rfree 20,32/25,03 rms bond 0,007 rms angle 1,363. I thought already one could maybe allow a bit more deviation for bond and angles.
well in this case it's hard to tell anything without looking at the files. What's happening shouldn't normally happen (based on what you explain) and if it happens then there must be a reason. If you want you can send me the files (model+data, and indicated the problem atoms) (OFF-LIST) and I will have a look. Pavel.