When setting a password, including < followed by a letter will cause an error to be displayed:

• If the browser is running on a client computer, then the error shown will be the “Something has gone wrong. We have logged this error for investigation” error, although no error will be logged
• If the browser is running on the same machine as the application services, then the error will be:
  
  A potentially dangerous Request.Form value was detected from the client (ctl00$MainContent$NewPassword="[your password]").
  
  Description: NET has detected data in the request that is potentially dangerous because it might include HTML markup or script. The data might represent an attempt to compromise the security of your application, such as a cross-site scripting attack. If this type of input is appropriate in your application, you can include code in a web page to explicitly allow it. For more information, see http://go.microsoft.com/fwlink/?LinkID=212874.

ASP.NET’s request validation sees the combination of < and a letter as potentially dangerous content, and so raises the error shown above.  For example:

• ‘Password<23’ is allowable
• ‘Password<bc’ causes the error

To work around the problem, do not include this character combination in your password.