This runtime error when exporting forms from the data tab is typically an Operation Timed Out error. This is likely the result of too many forms being exported at once. It often occurs when using the interface under the Detail tab of the Form Data.

To resolve, export fewer forms at a time, when using the Detail tab. There is not a definite number of forms which can be exported at once, as this varies based on the amount of data in each form. 

To export a larger quantity of forms, use the following location:
  1. Site Explorer>Forms
  2. Data tab
  3. Export & Print
  4. Enter criteria
  5. Click Export