Can't upload attachments in phpBB3

[seacuke]

Hello,
I can't upload attachments in phpBB3 (advanced plan, intermediate php).
Error log in CP shows "ALERT - function within blacklist called: passthru()" with following my own IP address.
Am I blacklisted, or my provider - what can be done to make the use of attachments possible?

Thank you.

My control panel: http://defineyourreef.x10hosting.com:2082
Website: http://defineyourreef.x10hosting.com
Forum: http://defineyourreef.x10hosting.com/phpBB3/