This may be related to the way Sql Server is setup to handle logins. Make sure you can login as a Windows user directly to Sql Server. My understanding is that SQL server can also be setup for only one type of authentication remotely so perhaps Windows Authentication is blocked when accessing the database remotely (like from PAM). So you might check with your DBA on this.
Other than that, make sure if there is a domain name involved in the user name that it is included correctly in the PAM operator. You might also check the database logs to make sure the userid is coming through as you expect it to.