@morrow without logs this will be hard to track down. can you ask your administrator to open up a support case for this?
Sending a file of 2Mb or larger using the Webaccess is not possible by default. This is caused by a limitation in PHP, which is the language used to build the Webaccess. The limit of PHP can be enlarged, but this should be done in the PHP configuration file.
When you want to send an email with an attachment larger than 8 MB, you can still use Outlook which doesn't have this limitation.
The value which needs to be changed in the php.ini file is: 'max_upload_filesize'.
max_upload_filesize = 16M