I think i figured out the issue(query timeout??) ...here is what i observed.
the customer BASE DN for User and group is different
-when i set the base DN to a level above where the group and users are available i always get the error invalid credentials.
-When i set the base DN to the level of User directory then i get "unauthorised" error
-When i set the base DN to group directory and below then i get "invalid credentials"
Is it possible to modify the plugin the mention both user and group base DN separately to avoid search timeout or hitting search limit.