Hi,
May be this because of the PERNR. When you enter the personnel number it is searching the PERNR. So, you settings for PERNR is external (External number range) for your 'EG' or 'ESG' . Check the number range settings and the NUMKR feature.
Also, check T529A table and see whether FC '0' has been set for the action.
Hope this helps..
Madhav.