Problem syncing project task list back in when using custom fields

Question

I have a project task list on Sharepoint 2010, which I want to sync to a Project file so data can be added back and forth. To add some custom fields, I have created a content type which inherits from the "Task" content type (from List Content Types) and added all the columns I needed for the future tasks. Now I can sync from Sharepoint to Project, but not from Project to Sharepoint. I am getting this error: "Unable to write information for task NameOfTaskHere to Sharepoint. Ensure NameOfTaskHere contains valid data and try again."

Is this because what was already in the task list is of the Task content type and that is no longer the default content type? (none of the columns added are required fields) I read that custom fields are to be added from Project and then sync to Sharepoint using "Manage Fields" - does it not work the other way around? Like making a custom Choice column so I can choose the options?

Or was my approach flawed at any point?

I am using Sharepoint 2010 and Project Pro 2010.

Edit: The same thing happens when I add columns to the project task list. Even if I check that the fields of those columns are not "Required" within the "Task" and "Summary Task" content types. So it's not just with new content types.

Answer 1

[Solved] The problem seems to come from a bug in Sharepoint where if a site column is listed a required, it will still show up as required even if the settings in the list are changed to optional.

Workaround:

• change the site columns to optional without updating all the previous content of those columns.

• create the list; now those columns will be optional

• set the site columns back to required; again, do not update the previous content