mod_security: Access denied with code 500. Error processing request body: Multipart: final boundary missing [severity "EMERGENCY"]

This error message from ModSecurity means that the request body was not
properly constructed or something was wrong with the file upload (most
likely that the client timed out and did not fully complete the upload).

Other possible reasons for this -

1) If the end of the final boundary is missing a CRLF
2) If the size specified in the Content-Length header is too small. In
this case, Apache would cut off the end of the file.

Known bugs
If you are using Apache with mod_security this will not work, you need to put the following in your .htaccess file to disable mod_security:

SecFilterEngine Off
SecFilterScanPOST Off

Disabling mod_security isn’t allowed on some shared hosts, and only do this if you know what you are doing.

So editing the .htacces is what i will do next