TOPIC: Conflict with private messages system

Hello, I've got really strange problem, when I try to read private message (administrator/index.php?option=com_messages&view=message&message_id=2) I get this error:

Fatal error: Cannot redeclare class idna_convert in /home/xxxx/public_html/plugins/content/smartresizer/smartresizer/idna_convert.class.php on line 54

when I disable the plugin I can read messages with no problems, I don't see how these two are related but still error is here

can someone shed some light on this matter