Maybe this is a late reply for Gaiser, but others who would follow the problem, I faced the same problem and got it resolved by granting Select/Edit access privileges to all JTX system tables from ArcCatalog -> Select Table, Right click -> Manage -> Privileges window.
We are having this same issue running Workflow Manager 10.4.1 on PostGRES. Is there a solution that is agreed upon for this thread? Could this issue be caused by multiple people using the sde schema to connect to the database with the .jtc file. Should I create a wmx user that we all use to connect to the workspace? Or should I create separate database users for each workflow manager user?
So what I did was create a new enterprise geodatabase using the sde schema; then that connection file is used in the Create Workflow Manager workspace. In PostGRS I created a login named 'wmx'. In ArcMap I set the workspace to the database connection and for each table I use the ChangePrivileges tool to grant view and edit access for the 'wmx' user. In workflow administrator each user will connect to the database using the wmx user. This seems to follow the online resource guide. If I encounter any more issues related to the schema error I will post them here.
What level of access do the users need to all of the Workflow Manager system tables?
ERROR: The current schema is out of date. Please contact your administrator to upgrade the schema.
When trying to connect to an upgraded database (10.2.1 to 10.6.1) in Workflow Manager Desktop.
The user properties under the workflow manager database connection must match the connection properties of the geodatabase.
For example: User Properties of the Workflow Manager Database connection:
Connection Properties of the Workflow Manager Database connection:
NOTE: When executing the Upgrade Workflow Database GP Tool, ensure that the aforementioned connections (see images above) match.