It may be you're not typing the password exactly the same as the actual password.
Remember, all passwords are "case-sensitive" - - uppercase and/or lowercase letters must match uppercase and/or lowercase in the actual password.
And where numbers are concerned, do not confuse a zero (0) with the letter 'O'.
If, as you suggest, it is the encryption type which is causing the problem, ask someone to change it to 'WPA' or 'WPA2' in the router's setup utility.