I have a table with col char(n) and I want to change its length to n+x. Why when i submit command:

alter table ... alter column ... set data type char(n+x)
e.g. alter table MYTABLE alter column A set data type char(25)

I get an error message:
SQL0190N ALTER TABLE "DBA.MY_TABLE" specified attributes for column "A" that are not compatible with the existing column.
SQLSTATE=42837

oops, I was doing it in our dev environment which is db2 v8.2. tried it in db2 v9.5 and it worked.