Do system tables get locked during truncates?

We have IDS 11.5.FC5 on our servers. We have been running a reload of Datawarehouse tables every night by truncating and Inserting the data for a few tables by pulling it from another database on a different server. The target db is local and readonly but still we revoke access to all during this timeframe partly due to the following issue but still are not able to avoid the issue. Occasionally we run into the error on a random table which seems to be a locking error. Not sure why would it happen even if we have exclusive access to the target tables. truncate tablename; 242: Could not open database table (owner.tablename). 106: ISAM error: non-exclusive access. Even having 'Set lock to wait' doesnt seem to help. I know truncate is a DDL, so would it be waiting on a system table to get exclusive access. Do you think the ISAM error actually related to the target table? Is there a better way to avoid it without major changes?