Comment 22 for bug 478717

The file wubildr must exist in the root of one of those partitions. e.g. /dev/sda1/wubildr or if you're looking on your windows drive C:\wubildr

If the file doesn't exist then you should copy it from the \ubuntu\winboot\ directory to C:\

If your drive is severely fragmented or depending on the physical position of the file (some bioses can't read beyond 137GB) it may not work. Try defragmenting in this case.