We've just deployed Kentico 9 in web farm mode to our production environment. Some users are experiencing issue with the reset password control on the login page. After they click the link in the email they receive an error is logged as follows:
Reset password control VALIDATIONFAIL Event ID 22778 Message: Request identifier hasn't been found. Exception type: System.Exception Event URL: /CMSModules/Membership/CMSPages/ResetPassword.aspx?hash=9f1312c4c6cbfd4aa92c4705ed929eb1b87c348965815fc17700080595e7734f&datetime=19082016154349&returnurl=%2fSpecial%2fLogin.aspx%3f.
I've checked that the Macro Salt is in the web.config and followed the instructions for setting up the web farm (machine keys, sticky sessions etc.).
I have faced this problem multiple times and the reasons is Macros. If you are using some in built Kentico control or custom.
Just go to System->Macros and re-assign all the macros from a user having Global Admin access level. This will make sure that your macros will not fail.
Sometime going to that field in the form control and removing the validation and re-applying the validation also solves this problem.