Level 3
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Their "alert" says that you can set the date, then disable conversion checking.

I believe the "correct" way would be:

1 - First, set the date to 4/15 or earlier

2 - Go to e-file and covert the return, but don't submit it.  This will check for all errors.  If you get any errors, fix these and check again. When you get no conversion errors, go back to the return and change the date to the date after 4/15 that you want to use.  Save the return, then go to E-file.

3 - Choose "convert and transmit" but disable conversion checking.  Otherwise, you will still get a conversion error because the date yet set is after 4/15.