You've probably already come across it, but for the benefit of other readers, ASE's rules for valid identifiers (object names) are documented in Reference Manual Vol 1: Identifiers
There is a solution that would let you avoid changing all the table names, which is to use the "set quoted_identifier on" option. See "Delimited Identifiers" However, you would then need to modify all your code to set this option on and put quotes around the identifiers, which is probably a lot more trouble than it would be to change the names to start with a letter.
-bret