That 1095A goes on the sons return also.  If parents already took 100% allocation, then you'd allocate 0% to the son (allocation is at the bottom of the 1095A)     

This thread explains how to make the software avoid the rejection with 0% allocation.

https://proconnect.intuit.com/community/proseries-tax-discussions/discussion/re-help-with-error-f896...