Implicit CAST is not working in Postgresql 8.4

I migrated data from Postgresql 8.1 to  Postgresql 8.4 using pg_dump.

But now I found that, most of the queries in my applicaiton are being failed. Invesitigating the problem, I found that no function is available in the DB to CAST INT to TEXT etc.

Most of the queries are failed because implicit cast is not working properly.

Any idea how to solve it.