Thanks for the reply, but this error message occurs even without file attachment.
The code is working partially: the message (and the file attached) are sent, althought the error message is showed.
Since xmailer uses the synapse libraries, i tried xmailer with the estable synapse and also with svn synapse.
I have another project in another folder which works fine using xmailer.
I do not see any diference between the two projects. Even the DLL libraries are the same version.
Thanks in advance for any help