I am running mxmlc in the command-line with -incremental=true. Flex is building the cache file using a checksum the first time. Subsequent compilations fail with this message:
Failed to match the compile target with path_to_cache/projectname_329043.cache. The cache file will not be reused.
My environment:
I just ran across this issue myself and after not finding the answer anywhere on the web, I bashed my head against mxmlc in practically trail-and-error until finding the answer. In my case, I was regenerating the flex config xml file each time I compiled from within ant. It turns out that this is the error you get in the case where it thinks the config has changed. You can test this by simply touching your config file and running against unmodified sources. So, if the timestamp is changing on your flex config.xml between compiles, that is likely the culprit.