VoipDiscount

Here's a fix:
1.Open Registry Editor (type regedit in start menu).
2.Locate HKEY_LOCAL_MACHINE\Software\Classes branch.
3.Check if mailto key is present and has a string value of URL Protocol attached. Note: keys are alphabetically sorted, so first there are the ones prefixed with a dot (file extensions), look for mailto farther down.
4.If HKEY_LOCAL_MACHINE\Software\Classes\mailto key is not missing in your registry, then the cause of your problem is somewhere else, try uninstalling IE10 (Programs and Fetures -> View installed updates -> locate IE10 and uninstall).
5.If HKEY_LOCAL_MACHINE\Software\Classes\mailto is missing as it was in my case, you have to restore it. In parent branch (Classes) right click, select New -> Key, name it mailto. In this new key create a string value (right click, New -> String value), give it name URL Protocol and you're done. Close regedit and see if it worked.