Data Manager has a small design flaw.
When doing the batch updates from Fidelity (I haven't tried other data sources), if a symbol produces an error, a Modal dialog window will pop up, thereby freezing the update until the window is dismissed. This precludes the ability to do an overnight update.

Since I am trading in a 1 minute basis, I have plenty of symbols where I collect 1 minute historical data. I am also noticing that running the data update 2 or 3 times is required before all of the data is properly updated.

Granted, I have yet to see a modal dialog window when a symbol produces an error. Which kind of error? Please post the message text, or include a small screenshot.

I've seen this occur before and have already waved a flag for it for the Fidelity guys, but I might not have done it officially or it could have been part of another bug report, so may have been overlooked. Please enter a support ticket with the details.