It's hard to say without having access to the content, but the first thing that comes to mind is file size. Do you have multimedia in these packages? What is the size of the compressed SCORM packages?
Having looked at the post Dave references, it sounds like a Flash runtime error. Might be good to access the content with Firefox + Firebug + Flash console, to see if there are any trace statements that can tell you what's going on in there.
You could also run the package through debugging to make sure there aren't any errors going on with comm through the API.