ER - Problem altering repliacted table

Hi all, We have ER running between two IDS 10 servers, 1 root (UC4)/1 leaf (UC5). When trying to alter a table (modify one column from smallint to char(5)), we get an error on the leaf server: SQL error 19995, and online.log says: 14:33:44 CDRGC: Alter mode set for replicate my_replicate 14:33:44 CDR GC: Can not verify grouper evaluation blocking status 14:33:44 GC operation alter mode set operation on a replicated tablefailed: CDR GC: Can not verify grouper evaluation blocking status The "alter table" works on the root server. What could be wrong ? Thank you, Philippe