Is there any method for the group founder to remove an owner?

[Cinnamon Lohner]

No.  All group owners are equal in status and once they are made an owner, they cannot be removed by another owner.  There is no special status for a group founder.  That's one of the reasons that you receive a warning when assigning someone the owner role so you are aware that you cannot change it once it is assigned.

--Cinn

[Cinnamon Lohner]

No.  All group owners are equal in status and once they are made an owner, they cannot be removed by another owner.  There is no special status for a group founder.  That's one of the reasons that you receive a warning when assigning someone the owner role so you are aware that you cannot change it once it is assigned.

--Cinn

[bee Baroque]

no group owners can be kicked out of the group. unfortunately in your case

could it be a solution to create a new group? or, if this person is breaking the tos i guess there would be no harm in trying an ar and have the lindens have a look.

[Silky Mesmeriser]

As others have already said there is no way to actively remove an owner once set, they would have you resign from the group or at the very least from the owner role themselves first before another owner would be able to remove them.  This is a necessary feature and provides the critical security necessary to have groups be useful for the holding of collectively owned land for example.

As for what to do about it then it is hard to provide any solid advice without some idea what "Actively causing problems" means.  Here are a few suggestions that might help but it is dependent on the circumstances:

In the event they are actually violating the community standards or terms of service you do have the option of filing an abuse report with LL, in the event that such abuse can be confirmed that might be one way to end the threat to your group as if their account is disabled it no longer matters they are "Owner".

On the other hand in most situations like this it is probably a matter of group politics, and there isn't an option to have the person forcably removed that said remember that normally you are dealing with someone who is a good friend or at least someone you are close to, you trusted them with ownership of your group after all.  In these sorts of situations I find that they can usually be resolved by talking patiently and politely with the person while keeping an open mind and try to bear in mind that no disagreement between two people is ever completely one sided invariably both will have made misinterpretations, over reactions etc which added to the conflict.

So I suggest you try sitting down and talking calmly with the other owner and try to find a solution you can both live with that produces the best outcome for the group and it's members.  If the situation has become heated try taking 24 to 48 hours away from SL and come back with a clear head and be ready to compromise you can probably find a solution to this.  If you like then I may be able to help provided that both of you are willing to at least try to reach a compromise, I have pretty good diplomatic and mediation skills and am happy to use them to help others provided that both sides genuinelly want to try (If not then it's pointless) contact me in world if you would like my help/advice further.

If all else fails the final option is to fork the group, create another group and ask your existing members to join that new one, it is a drastic action though and it will cost you a portion of your membership so it should be a last resort.