What type of client are you using - full from the regular install or the instant client?  Also are you using the tnsnames.ora for your instance naming?  I know when I used the instant client recently, I needed to define both ORACLE_HOME and TNS_ADMIN so that it would work.For example, I had the following set up as user environment variables.ORACLE_HOME=C:\instantclient_10_2TNS_ADMIN=C:\instantclient_10_2\network\adminNS_LANG=AMERICANDepending on the type of server, you may need to restart the service for the environment variables to refresh as well.  I vaguely remember having to restart all of IIS to get it to connect.