Error installing collector: "Failed to get_available_oracle_homes on Middleware host ..." (4267454)

Error installing collector: "Failed to get_available_oracle_homes on Middleware host ..."

The full error message from installer.log:

Wed Mar 30 13:36:09:727 2011: EXCEPTION
Message(SCException): "API function: "Retrieving installed Oracle homes" ("getOracleHomesInternal") Failed. Return Code: "-9999", Return Message: "Failed to get_available_oracle_homes on Middleware host hostname.domain.com""
Message(User): "An internal issue has occurred.
Please retry the last operation to continue the installation process.
If this attempt also fails, please contact Quest Support."

Mismatched 32-bit Oracle client with 64-bit Middleware installation.

Install 64-bit Oracle client on Middleware machine to use with 64-bit Middleware agent.