You currently have the ORACLE_HOME environment variable set on your computer. Setting this variable:

• Is not required for Oracle products to function properly. Oracle products find the value of ORACLE_HOME in the Windows NT registry at the location specified by the ORACLE_BASE\ORACLE_HOME\BIN\ORACLE.KEY file.  Setting the ORACLE_HOME variable in the environment is not necessary or recommended.
• Prevents multiple Oracle home environments from functioning properly. The conflict occurs when you set ORACLE_HOME to point to one Oracle home directory, then attempt to run programs from a second Oracle home. These programs first check for any environment variable settings (such as ORACLE_HOME), before checking the registry through the ORACLE.KEY file. Since ORACLE_HOME is set, the programs in the second Oracle home attempt to use files in the first Oracle home, causing a conflict.