can't add new column to table in replication

I have a merge replication running and when I try to alter table with this commancd:

alter table mytable add cTestColumn nvarchar(10)

getting this error:

Msg 21531, Level 16, State 1, Procedure sp_MSmerge_altertable, Line 378
The data definition language (DDL) command cannot be executed at the Subscriber. DDL commands can only be executed at the Publisher. In a republishing hierarchy, DDL commands can only be executed at the root Publisher, not at any of the republishing Subscribers.
Msg 21530, Level 16, State 1, Procedure sp_MSmerge_ddldispatcher, Line 191
The schema change failed during execution of an internal replication procedure. For corrective action, see the other error messages that accompany this error message.
Msg 3609, Level 16, State 2, Line 1
The transaction ended in the trigger. The batch has been aborted.

I tried to drop the sunscription and publication and even after that I was not able to add the column or rename the table !!

I create a test db on the same server and everythign worked fine on test db

what is going on with my DB ? how can I get it reslved ? it's happening with almost all tables and not a specific table !!

any hints are valuable since I'm stuck and don't know how to progress

thank in advance,

Patrick

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Patrick Alexander