The problem is due to an incorrect setting for the RTF IFilter. On some Microsoft Office installs Word takes ownership of the .rtf file format but doesn't actually accept the file format when used in IFilter mode. You can verify this is the problem by opening Configuration and looking in the IFilter list. If the 'Microsoft Office Persistent Handler' is registered for RTF files then you have an incorrect setup:
To fix this you'll need to re-register the RTF IFilter. From an Administrator command prompt type:
If successful you should get a message saying 'DllRegisterServer in C:\Windows\System32\rtffilt.dll succeeded.'. Re-open FileLocator Pro and look at the IFilter configuration. It should should now report something like 'rtf persistent handler' against the rtf file type.
RTF file searching should now work (assuming that you have activated Office/PDF document searching in the Options tab).