Connecting to a 10g database with 10g client results in error "OCI version 10.2.......... <about 20 numbers> is not supported". The 'Connect Using' drop down in the login window shows the Oracle Root in RED but the 10.2.0.2 client is valid. Select the 10g client results in the error message.
Ensure the valid Oracle client is at the beginning of the PATH environment variable. e.g.
1. <Right Click> My Computer | Properties | Advanced | Environment Variables | System Variables | Select 'Path' Edit
2. If the Oracle Home exists in the 'path' string, cut & paste it to be the first entry in the string. Otherwise add it.