GMX does not offer new account registration in all countries, so this is one possible source of a sign-up error. However, if you are trying to register in a region where GMX is available, the error may be due to the IP address, password or email address.
If the error persists, we suggest you wait 24 to 48 hours and try again using a different IP address or internet connection, and, if possible, another computer. You should also make sure you are using the latest version of the internet browser.