Humm,
There is such a thing as group owner permissions. Not talking UBB but for example ftp.
If your host changed them them you are no longer the owner of the file no matter what permissions the file is set to.
I have seen that happen on a windows server but not linux.
When you say you can't delete one, but can upload.
Do you mean all existing and new files will not delete.
FTP to the account and see if you can manualy delete one.
If you can see if the group setting is different from one you can't.
