Apple recently added a new way to share files via your MobileMe iDisk. It is ideally suited for those times when a file is too large to include as an e-mail attachment. With this new method, you can opt to share any file from anywhere on your iDisk. MobileMe creates a download link for the file, even assigning a password if desired.
When I tested the feature out, I could not get it to work consistently. Sometimes it worked just fine. On other occasions, when I selected to download a file, it appeared on my drive with an extension added to its name (either .html or .txt), even though the original name did not include the extension. These files would not open properly, even after removing the unwanted extension. For example, I deleted the .html extension from a downloaded PDF file, leaving .pdf as the active extension. When I attempted to open the file in Preview, a message appeared that said: "Couldn't open the file. It may be corrupt or a file format that Preview doesn't recognize."
As it turns out, the problem is not specific to downloading files via a MobileMe assigned link. That was just how I first tripped over it. The same symptom occurs if I directly select to download the file from the Web via MobileMe's Download button. However, if I instead use the iDisk command in the Finder's Go menu to mount my iDisk, the same file downloads from here without any problems.
An Apple support article notes that these sort of symptoms can occur when downloading shared files from MobileMe--if certain characters are in a file's name. In particular, if a name starts or ends with a space, or contains a carriage return, the file will not download. The solution here is obvious: Eliminate the offending character(s) and try again.
These characters were not in the names of any of my problem files. Still, the symptoms do seem to be linked to a particular file or type of file--as one downloaded item would consistently fail to open while another one consistently succeeded. In my testing, Safari webarchives were especially prone to these problems.
There appears to be a related bug that involves uploading html pages via MobileMe (as described in this discussion thread post), but this is not the same as the download problem described here. Beyond this, I have been unable to isolate precisely what determines success or failure. If any readers can shed further light on this matter, I'd be pleased to hear from you.
This story, "Bugs & Fixes: When Mobile Me File Downloads Won't Open" was originally published by Macworld.