I cannot activate my account, the link i got in my email sais this:

Error: invalid call of page!
Notice: Undefined index: hash in /home/nexuiz/domains/planetnexuiz.com/public_html/ladder/includes/unlock_account.php on line 14
Error: invalid hash value!

is this a temporary website bug or something?

It shouldn't be a temporary website bug. However, it shoudln't be the case that both errors occur at the same time ("invalid call of page" and "invalid hash value". What was the exact link in the email ?

well, http://www.planetnexuiz.com/ladder/?p=U ... 18c4354d77

try to replace them "&" with a "&". I'll check that some time if the mail is corrupted, if not, it is your email software that messes with the html format of the mail

EDIT:
I checked the script code and it seems to be alright! It must be your Email-Software messsing with the URL. I activated the account for you by entering http://planetnexuiz.com/ladder/?p=Unloc ... 18c4354d77 into the browser. It is now activated.