No more available UIDs?

Hi all, today while installing Citrix Workspace, the post-install script gave me this error: useradd: Can't get unique UID (no more available UIDs) useradd: can't create user So I examined the script, and saw that the command producing the error is this one: useradd -d /var/log/citrix citrixlog Trying to execute it at the cli gives the same error. This are the contents of /etc/login.defs FAIL_DELAY "2" GID_MAX "0" GID_MIN "0" PASS_MAX_DAYS "0" PASS_MIN_DAYS "0" PASS_WARN_AGE "0" UID_MAX "0" UID_MIN "0" Google does not help. What could be the problem? Thank you in advance Cris