DataSource.Error connecting to SharePoint 2010 list

I was having this same issue on two particular lists on our SharePoint 2010 site. I read some posts that mentioned it could be caused by lookup fields, but neither problem list had such fields. Other posts mentioned people/person fields, I had them but I ruled that out as well.

So I turned to the calculated columns in my list. I had three. I set each one to just a calculation of "=1" and saved, and noted that the ListData.vsc started working!  While two of the calculated fields had much more advanced formulas, after process of elimination I determined that this calculated field is the one causing the problem for me:

Field Name: "Expected Launch Date"
Field Formula: =IF([Call 2 Completed]=0,"TBD",[Call 2 Completed]+7)
Return Type: Date Only

You might see the problem now -- my simple "IF" formula is returning text "TBD" string for a column with a type that must return "Date Only". So, I changed the formula to the following and my list is still working now.

New Formula: =IF([Call 2 Completed]="","",[Call 2 Completed]+7)

Read as "If [Call 2 Completed] is null, use null. Otherwise, add 7 days to [Call 2 Completed]"

Anyway I think I'm good now.