Some users are reporting problems when using Windows (XP only so far) and Internet Explorer 7 or Firefox 3.  When sending a message with attachments, one or more will fail with the message:

And then the remaining attachments may or may not be processed successfully.  Finally this message is shown:

"There was a problem uploading the file.  You have exceeded your file storage limit.  We are unable to proceed with sending your message."

The code 2038 is a flash specific error and appears to be related to a failed upgrade of Flash.  Here are instructions on resolving the problem:

1. Uninstall Flash.  Download the flash uninstaller here: http://kb.adobe.com/selfservice/viewContent.do?externalId=tn_14157&.... (It is vital that you use this flash installer and to not use the "Add / Remove Programs link in the Control Panel.  Not all files will be removed using "Add/ Remove Programs.")
2. Close *all* Programs.
3. Run the Flash uninstaller.  View the details to make sure that everything completed correctly.
4. Reboot your computer.
5. Install the latest version of Flash (currently 10) by visiting http://get.adobe.com/flashplayer/.
6. To confirm the version of Flash installed in your browser, visit: http://www.macromedia.com/software/flash/about/.

Make sure to follow these directions to a T.  The first time I tried, I skipped rebooting and the problem did not go away.  I had to perform the whole process over again.