A table in replication cannot be truncated, due to truncate being a minimal logged operation and this the full delete pages not logged in a fully logged operation so CDC or replication doesn't know how to handle it.
select * from sys.messages where text like '%change data capture%' and language_id = 1033
The above will spit out the messages / errors pertaining to CDC, some noticeable ones, you can't use column sets, cant truncate the log as the log reader isn't running etc.
Take a look through them to see what warnings/errors can come out from SQL relating to CDC.
But my question is why would you want to truncate a CDC enabled table, you're not getting the delete history, do you actually need CDC on it?