you may have a corrupt fla.
save your current fla to a different directory and with a different name. then click file/save and compact. then close your flash ide.
re-start your flash ide and re-open the newly named fla in the new directory. try adding a new keyframe.
if that works, you can save it back to the original file name in the original directory.
Thanks for the reply.
It seems like I have a problem with Flash in general as its crashing a lot lately. I was able to work around the issue by removing the MC, adding the keyframes first and then dropping the MC into the scene.
I have a new problem now, how can I export my Movie Clip as FLV? When I go to the export movie option, it supports many formats (avi, mov, gif etc.) but there is no option to export as FLV.
Any idea how to do this?
export as an avi or mov and use media encoder to create an flv from the avi or mov.