User has access to webview report However, the problem appears when user try to customized any reports by using InfoMaker.
error appears saying "domain\user" is not a valid user in database Instance_HDS
Sounds like it's saying you have a permissions problem at the SQL level. Apparently you have your system locked down and the user doesn't have the necessary rights to the HDS database.
This is a SQL server issue where you'll need to add the user under the security section of the SQL Enterprise Manager, or use a user account that has the necessary rights.