On a ASE 12.0, a request with a clause 'in' exceeding 250 values returns Error 404 (Too many ANDs or ORs in expression (limit 250 per expression level). Try splitting query or limiting ANDs and ORs.).
On a server, a similar query with more than 250 value in the 'in' didn't return an error. But is there a limitation on the number of value on an 'in' for a ASE 12.5.0.X and above.