Could you try to log in to your site via FTP, delete the existing Jetpack folder, and reinstall the plugin manually as explained here:
http://codex.ww.wp.xz.cn/Managing_Plugins#Manual_Plugin_Installation
Let me know if it helps.
I think your site may have actually been hacked.
The file class.jetpack-error.php should only be three lines, as you can see here:
http://plugins.trac.ww.wp.xz.cn/browser/jetpack/trunk/class.jetpack-error.php
A malicious attacker may have compromised your host and appended unfriendly code to the end of the file. I’d recommend a security audit, or at the very least installing a security scan plugin such as VaultPress or any of the free options in the plugins repository.
Hi Jeremy and George,
Thanks for your quick reply.
The strange thing is, I one of the sites had the same issue last week. I have deleted and reinstalled and it was gone. Now it is back, but in the file on that server are only the 3 lines.
In the other website indeed is a whole list of code trying to find out what kind of software visitors are using.
Scary.
I will remove jetpack on both sites imideately and reinstall after I double check the security plugins.
Thanks, so much for your help.
