Can't create connection in Toad for Oracle freeware

when attempting to create a connection, i get the message “You do not have an Oracle homes installed!”.

i have the instant client installed, there are two instances setup which test fine in the odbc config section. tns_admin is defined as an environmental variable and points to the correct place - c:\windows\oracleODBC\network\admin - which is where the tnsnames.ora file is stored.

what else could possibly be wrong?