Description:  When a user goes to the reset password page and provides user id, results in an error 

Application error. Please contact the FlexNet administrator. (platform.exceptions.MultipleDataFoundException)

How to resolve this error?

Resolution:  As the error message states, multiple user records exist in the database and the application is unable to uniquely identify the user.

Run the following query to take a look for any duplicate entities in the user table
select * from PLT_USER where USERID = "username"

The query should return multiple records in the table. Delete the duplicate rows to resolve the issue.