Hi Maria,
against common belief, most error situations are not deat with properly in PA-OM integration and therefore the reports mentioned by Rohiy need to be use don a regular basis to guarantee data integrity.
Some situations, where integration can go pear shaped are missing authorisations, a position marked as obsolete or a configuration error on "the other end" of integration (more likely to occur, when you make the change in PPOME and then an error in the PA infotype such as a newly mandatory field not filled in existing records leads to PA not being updated.
In your example, missing athorisations are something you should check. Does SU53 indicate any issues, when such a "broken" data change is peformed?
A very simple possibility would also be yoru integration config: are you sure the employees in question are technically integrated according to the current version of feature PLOGI?
kind regards
Sven