Custom web part saves custom field results in project out of date error

Question

We've created a webpart and user control that uses a sharepoint people picker to save AD accounts to a project custom field.

To save, we've hooked into the ProjectSave event (click 'Save' on the ribbon) using a page component.

After the save callback is triggered and we've updated the custom field, PWA complains that, "the project is out of date" and has been, "updated in another session." That's obviously our doing.

Our suspicion is that someone tracks the last updated date/time and notices that it's changed since being created.

Thanks for any suggestions.

Update

void OnSaveProject()
    {
        ProjectDataSet projectDataSet = ProjWeb.project.ReadProjectEntities(ProjectUid, (int)(ProjectEntityType.ProjectCustomFields | ProjectEntityType.Project), SvcProject.DataStoreEnum.PublishedStore);
        //ProjectDataSet projectDataSet = ProjWeb.project.ReadProject(ProjectUid, SvcProject.DataStoreEnum.PublishedStore);
        ProjectDataSet.ProjectRow project = projectDataSet.Project[0];

        if (!project.IsPROJ_CHECKOUTBYNull() && project.PROJ_SESSION_UID != null)
        {
            Guid fieldGuid;                

            // skip if this customfield is not set
            //
            if (!String.IsNullOrEmpty(ProjectServerCustomFieldAccounts))
            {
                fieldGuid = ProjWeb.customFields.GetCustomField(ProjectServerCustomFieldAccounts);

                if (!ProjWeb.SetCustomValue(projectDataSet, project.PROJ_SESSION_UID, fieldGuid, PeopleEditor.CommaSeparatedAccounts))
                {
                    PpWebPart.Log("Error at SetCustomValue to value" + PeopleEditor.CommaSeparatedAccounts);
                }
           }
        }

Then, SetCustomValue:

public bool SetCustomValue(SvcProject.ProjectDataSet forProject, Guid sessionUId, Guid field, String value)
    {
        Guid ciJobId = Guid.NewGuid();

        foreach (SvcProject.ProjectDataSet.ProjectCustomFieldsRow r in forProject.ProjectCustomFields)
        {
            if (r.MD_PROP_UID.Equals(field))
            {
                if (r.TEXT_VALUE.Equals(value)) return false;
                r.TEXT_VALUE = value;

                project.QueueUpdateProject(ciJobId, sessionUId, forProject, false);
                queueSystem.WaitFor(ciJobId);

                return true;
            }
        }

        return false;
    }

Answer 1

Make sure that your custom Save logic isn't calling Update(). If it is, then what is happening is that the page is attempting to save from the known state 'XYZ', hits your Update() which then changes the underlying item from 'XYZ' into state 'ABC'. However, the Update() from the submit itself hasn't fired yet. When it does, it is expecting to update item in state 'XYZ' but instead finds state 'ABC'. To the code, this means that the underlying item has been changed which means that the changes being submitted contain outdated data along with the updates. SharePoint fails the second update in order to prevent data loss.