Not much code to draw any conclusions on, but let’s give it a whirl.
I assume you have an RPG program that has an F-spec with file OUTRRX as an output file. Is this described as an externally defined file and is that file a source physical file? When a source file is created it is given the same record format name as the file name so this file would have a format name of OUTRRX. So if you are creating a source file named QRRXSRC in QTEMP prior to overridng, you are trying to override format OUTRRX with a file that has a format name of QRRXSRC which could be giving you the format error. Instead of using CRTSRCPF to create the QRRXSRC file in QTEMP, do a CRTDUPOBJ of OUTRRX and name the new QTEMP file QRRXSRC. This way both files will have the same record format name.
Hope this helps.