Hi I've wordpress site. I've installed modern-blue-eco-friendly-120070612-2 theme.I quickly got a mistake message around the right hands side "Fatal error: Call to undefined function cypher_previousposts() in mydomainwp-contentthemesmodern-blue-eco-friendly-120070612-2sidebar.php online 59.

Does anyone know this? Help me ....

Thaks ahead of time

cypher_previousposts appears to become from a plug-in named "Previous Posts" (see e.g. here). The writer appears to become running the website cypherhackz.net. I'd recommend you look for this wordpress plugin within the official Wordpress wordpress plugin repository and do the installation after that.