Does TNSNAMES.ORA of the Developer Suite 10g contain entry for the database you are trying to connect to? Compare 9i and 10g's TNSNAMES.ORA files! Also, you might be interested in maintaining only a single copy of the TNSNAMES.ORA file; if so, search for the TNS_ADMIN environment variable and the way it is to be used.
I have installed Oracle 9i in my system. Later I have installed forms 10 on the same machine. Even though I can able to access 9i with basic scott/tiger
im unable to get into forms 10g. When Im trying to get into forms 10g with same scott/tiger. Im getting the erro message as tns could not be resolved.