I have found that since trying a certain password logging into the Web Access for RDS 2012 R2, an error is generated.
It doesn't crash the server it just causes an error for the user logging in.
Sign in either as with domain\username, or upn, and using the password ")<bJKq<5" without the quotes, doesn't report wrong password but instead gives the error "Server Error in '/RDWeb/Pages' Application"
This happens whether you enter the password for anyone trying to login.