You should be able to re-enchant equipment as much as you wish, as long as you have the required ingredients for the type of enchantment you want to use (from the list of what is available).
After un-enchanting you need to back out of that interface, and choose enchanting from the option menu. If that doesn't help, try exiting the conversation completely, and then talk to the enchanter again.
In the enchanting interface, does the un-enchanted piece of equipment not show up at all, or is it listed as 'whatever (0/1)' but still greyed out?
Maybe try asking in the German forum, in case this is a known issue in that version (though if so I would think the patch should have fixed it).
You can not make charms. Divine charms (the best available) can be dropped by certain boss type opponents. Other types can be found or purchased (ie from the jewelry merchant in Aleroth, available later in the game). At the end of Broken Valley, and after clearing some of the fjords, I had 3 blessed charms, 3 major and 4 minor.
