What is the file size of your DDR?
Does it not go away after rebooting your system?
I would try doing a deep level trawl in your OS for any temp files of the same or similar name to get rid of. Also, clear your browser temp files cache and then restart.
Also, switching to XML based DDRs and using the blazing fast FMPerception product to read them out may be a long term solution towards DDR usability and your own sanity. Depends on what you are using DDR reports for, but I have found it invaluable.
Additional advantage to moving to the XML-based DDRs: My experience has been that the XML DDRs output noticeably faster than the HTML DDRs.
Disclosure: I'm the developer of the above-mentioned FMPerception.