We had to go to Microsoft for this solution so I can’t take credit for it but I wanted to post the info here for others who may run into it.
We have a couple lists that have many columns (70 90, roughly) with various data types. At least one of the columns has the option set to allow multiple selections, like on a Person/Group column. There is a workflow attached to the list. It doesn’t matter what the workflow does, could be updating a column value, sending email, whatever.
At some point the workflow fails to complete and throws an error. Diving into the workflow tasks for the item the only error shown is "Unknown Error". Very helpful. This error results regardless of how the workflow starts, either manually or automatic.
Before we opened a case with MS I did some work to try to duplicate it. Creating a large list with many column types worked just fine, regardless of combination. The only way I could re-create the issue was to use a list template created from a list that was already showing the symptoms.
Once we brought in MS we narrowed the error down to workflow’s created within SharePoint Designer. That was a good step in the right direction.
My next MS contact was from the Designer team. He was unable to duplicate the issue by creating a list from scratch as well, but could duplicate it using the list template I provided. Below is his solution to get the list back to allowing workflow’s without error.
This may be more of a work-around than a solution, but it gets the job done. Basically, it involves updating the multi-select column value to itself within the workflow along with whatever else the workflow is doing. If you have many multi-select columns it may take you a couple tries to find the culprit, or you can just do this to all of them and be sure you got it. It doesn’t hurt. Here’s the process assuming you have a People/Group column:
- Open the workflow that is having issues and click the Variables button at the bottom.
- Click the Add button and give the variable a name and a type of string.
- Add the Set Workflow Variable action to the top of your Actions since we need to use that variable in the update action.
- Set the workflow variable to the current value of the list column by choosing Current Item as the Source and the list column as the Field
- Modify the current update list item action (or add one if you don’t already have one) to include the values you want updated. The order doesn’t seem to matter, so just click the add button.
- For the Set this field drop down select the name of the column that has the People and Group type.
- For the To this value click the fx button and select Workflow Data.
- For the Field select the variable we created earlier and click Ok. Keep clicking ok and eventually click finish. At this point your existing list should work.
How does the list get to this corrupt state in the first place? It’s not related to the number or type of columns. If you have any ideas please contact me or leave a comment.