Table Versioning Controls Access to Join Indexes

Any table is only available for write use to a single user at any given time.

For join indexes, this means that when one user is updating any table in a join index, no one else can update any of the tables in that index. All the joined tables remain unavailable until the first user's transaction is committed and you have synchronized the tables with the SYNCHRONIZE command.

Other users receive the following error while the join index tables are in use:

Cannot write to this table in current transaction. 
Another user has write mode access.

Their current transactions cannot write to any of the join index tables; they must begin a new transaction to write to those tables.