No Entry by Roster

Hello,

we are working with wildfire + ldap (active directory).

Since 2 weeks we have a problem.

three users have no online contacts in her spark.

if I look at the wildfire Server in the “Roster” I see no Entry.

Everyone in the company have everybody in the Roster, only this three users have no entry.

Is it a possibility to change it?

Many Thanks

Sylvia