device space on creating index

Hello, everyone. We have an informix database server. Recently, we just recreate all the tables. There is one table don't have index key. When we tried to add index using sQl command, it returns message say "no device space". We think we have enough disk space, is it possible that we don't have enough table space for this table and couldn't add index to the table.. What we should do and how we can solve this problem to add index key in. Thx, Tina.