I've had this happen to a few documents opened in Flash Pro CS4 and CS5.5. It looks like the issue is with the paths to library assets. For instance, If I have imported a jpeg file and then move the folder that the original jpeg resides in, Flash may give me this error the next time I start it and open the FLA file that uses that asset.
So the short of it is that Flash is giving an unhelpful and possibly misleading error. The solution seems to be to walk through your FLA file's library and relink assets that seem to be missing their content. Or start over from scratch if you're a glutton for punishment.
The long of it is that, if I look at the properties of an errant library item, what I see is an absolute path to it's source. That probably means that if I take the project and it's assets anywhere on a portable drive then there's a fair chance I'll break the project. And if I move a folder full of source assets in relation to the FLA file then Flash will definitely give me this error. Although it may be that flash is storing absolute paths and calculating relative paths before trying the absolute one
Furthermore, the absolute path Flash is giving me is like .\d$\remoteFolder\remoteFolder\myFile.png. If I relink the library item to the asset the path gets rewritten as \\myServer\remoteFolder\remoteFolder\myFile.png
Anyway, at the very least it'd be better if Flash could come up with a better error message. Ideally, It'd give you a dialog list/table of all the mislinked library items and help you to relink them quickly.
i've not run into that problem and i routinely move files from my home and work computer which invalidates all the imported asset paths.
i would think those paths would only be a problem if you tried to "update" those assets without correcting the path.
Yes, I'd agree that it shouldn't be a problem until you manually update the paths of the library items to the assets. Usually that's what seemed to be happening, but in this case, and with several FLA files, Flash appears to be checking those paths when it opens the files, and then if the check fails then I get the error message and I end up with some bitmaps in my library that don't have any bits in them.
The thing about Flash using absolute paths may be a red herring. It seems like the first thing it does is check paths in a relative way even though the path is not listed that way in the library item's properties. It's not very transparent, whatever it's doing. (actually, I guess I have no idea what Flash is doing under the hood.)
So, on reflection, the problem probably stems from moving a folder full of assets in relations to the FLA files using them. But still, I'm really surprised that Flash is just leaving empty bitmap items in the library when it can't find the original assets. In past experience Flash would just keep the library item as it was and the problem would only turn up if you tried to update the item.
You mentioned that you were seeing this issue in CS5.5. Can you check the version number in the about box for me? Is it showing 11.5.0 or 11.5.1? We are aware of this issue and have released an update (11.5.1) for CS5.5 to fix this. If your version is 11.5.1 and you still experience this issue, please email the complete step and or file to me at FlashAuthBetaBugs@adobe.com. Before emailing please zip your file, change .zip extension to .zzz and send me that.
Flash Pro, QE