When trying to connect to an Oracle database you receive the following error: "OCIEnvCreate failed with return code -1 but error message text was not available"
One of the two following circumstances is the likely cause:
1, You are using an unsupported version of the Oracle Client (older than 11.2) on Windows 7.
2, DLLs from a previous installation of Oracle Client have been left on the system, causing a conflict.
1, Install a supported version of the Oracle Client.
2, Perform a search for "OCI.DLL" on the local machine. If you find any instances of this file in any location other than your ORACLE_HOME rename or delete it. If in doubt, uninstall the Oracle Client, then perform the search again. Anything that is leftover is the culprit.