If receiving an error similar to the following in QuickBooks Web Connector, see these steps:

Error: 3391 - The iteratorID "{cc52ba2e-81a2-4116-bd8d-6185ab84c739}" is not valid.

We've seen this error happen during (at least) two scenarios:

- The communication is interrupted (internet connection drops).

- A modal window/dialog is opened in QuickBooks Desktop during a sync.

A "modal dialog" is the type of window that appears and you must either hit OK or Cancel to close the window and its the type of window that you cannot put behind another window.

A good example is the Edit > Preferences window in QB - that is a modal box. You must either OK or Cancel out of that window and if you click anywhere else in QB there is an audible ding.

In summary: QuickBooks cannot run two actions at once.

Resolution: Close any modal windows in QB and retry your operation.