I get that sometimes. Regarding the timeline, are you sure you aren't putting it in the timeline "bin?"
There are now tabs for TIMELINE and BIN where there used to only be BIN.
Sometimes viable clips won't load in RCX. I've noticed that for a while. I have found that if it doesn't load in one version, it will load in another. Try using an older version, like 326 or even back to 262.
Don't know why this happens but about 1 of 20 clips of mine won't load in various versions.