[Samba] change primaryGroupID - unwilling to perform

[Lars Hanke]

My tool is growing fast and it takes me to the finishing line for 
setting up my new user database. But nw I came across another strange issue:

I'd like to change the primaryGroupID. It is currently set to 513, which 
simply does not exist. I wanted to set to 100, which exists and actually 
the user is a member of this group, but then I get the following exception:

ldap.UNWILLING_TO_PERFORM: {'info': 'error in module samldb: Unwilling 
to perform during LDB_MODIFY (53)', 'desc': 'Server is unwilling to 
perform'}

This is the equivalent LDIF:

dn: CN=Lars LH. Hanke,CN=Users,DC=ad,DC=microsult,DC=de
changetype: modify
replace: primaryGroupID
primaryGroupID: 100

Any ideas, why this is prohibited?

Regards,
  - lars.