As a wild guess, try changing the name of the second instance of the table even more such as CSPONEMPS in case it's only seeing the first x number of characters and doesn't realize that you are doing a self join.

I've not used ViewEditor or FireBird but something is realizing that the two tables in select are the same physical table and is trying to "help" in the wrong way. Hopefully someone has a better answer.

Good luck.

Jason