All I can think of is that as the forum is part of a standard Oxwall installation, and groups are not, that the groups plugin has to be installed after the forum plugin to pick up on any forum content. This may well not be the reason though.Have you tried deactivating (not uninstalling) and reactivating the groups plugin?
Yes i tried deactivated, its the issue in the DB - as you rightly said,
this is what happened unknowingly :-
Step 1)Installed oxwall, did all basics reculsive 777 etc.. added forum, group, and events!
Step 2)Created few groups as per client requirement, around 20 of them and added forum in each group for users
Step 4)Due to some reason since it was not being used, i had to uninstall forum (it was not needed that time)
Step 5)Now when re-installed forum, all old group are not showing forum
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New Problem: Over and above this now when trying to create a new group it is throwing error500
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I am shocked no one noticed this and never came-up with this problem ? Someone out of you all great developers need to find out exactly how the two plugins interact with each other and write a tutorial on how to solve this issue...