Tested in IE 8 and Firefox 3.6.13.
Meldung: Hexadezimalziffer erwartet
I think it translates to "hexadecimal number expected"
In Firefox I used FireBug to track the load process. I tested different files, varying filesizes, etc. It seems that it is a problem with certain files but I couldn't find a rule for that (e.g. filesize greater than x MB)
This is the error :
* doUpload File Dropbox 1.0.10.exe
single file - do upload, fieldName flashUploadFiles
** onProgress ** 0.004453684292934125
ioErrorHandler: name=Dropbox 1.0.10.exe event=[IOErrorEvent type="ioError" bubbles=false cancelable=false eventPhase=2 text="Error #2038"]
After that a timer ticks from 1 to 599 (10 minutes). During this time the browser "hangs". What happens then depends on if you try to upload one or more files.
If this is the only file, you get an error "Could not find File Upload Document" and the browser hangs (page is inactive).
If there are more than one file, the process continues with the next file or saves and sends the mail. The file with the error is missing in the upload document.