This error usually occurs when the perimeter of the truss or a member can not be determined.
You can turn on the analog to see if it indicates where the problem is or simple trim or re-add any members that appear to be causing the issue.
Things to look for:
-Webbing that is not trimmed correctly.
-Multiple pieces that are coming into the same location.
-Look for a piece that is not being analyzed.
The circled piece below is not being analyzed.