During FMW components installation, you might hit this problem while reinstalling the OSB or SOA product inside fmw folder second time.
The reason for second time installation could be anything e.g. Oracle_SOA1 files got cruppted, last attempt installation was not successful etc.
In my case, I got stuck with Eclipse client installation, I did eclipse installation once I finish Oracle Service Bus Installation, as result OSB perspective was not appearing while I was running eclipse indigo GUI.
In order to fix this problem, I need to first install Oracle Enterprise Pack for Eclipse 11gR1 (184.108.40.206) (for Oracle Service Bus 220.127.116.11)
and then Oracle Service Bus, when I tried reinstalling Oracle Service Bus then got below Error.
Now, to fix this problem I have made two changes as describe below -
Updated the "inventory.xml" located inside $Middleware_home/ContentsXML" directory as highlighted below.
Just commented the lines which has reference for "Oracle_OSB1" word.
renamed the existing Oracle_OSB1 to "Oracle_OSB1_bkp" and Moved the existing Oracle_OSB1 folder to outside Middleware home folder.
e.g. "mv Oracle_OSB1_bkp11032015/ ../../"
That's it, once we do above two steps, and re run the installer of Oracle Service bus and it does not give Oracle_home already exist error.
In case of Oracle Service Bus installation, choose the existing OPE location this time and continued the ORacle Service bus insllation.