Jacob,
The warning in the diagnostics tells you that although the beam has stiffness and mass, it doesn't have any points defined by the user at which to calculate beam results (deflections and stresses) to display. The user is not obliged to define recovery points for a sketched beam and not having them keeps the results files a tiny bit smaller.
As to whether this is the cause the fatal error I don't know but would experiment a bit (I have a nagging at the back of my mind that I have seen similar when using a sketched beam section).
- Can I repeat the failure with a model containing a single beam that has no recovery points? (the modal plots won't be exciting))
- Add recovery points and see if the issue goes away.
- If the problem goes away with the single beam, put recovery points into the beams in your big model and see if the problem goes away.
- Exchange your sketched beam in your big model for a approx. equivalent standard section and see if the problem goes away
- Pass all of the above on to technical support and keep us all posted
Regards