What are some solutions or cause for this error message:
"Model is unstable. Restraints may not be adequate."
try using soft spring to stabilize model or use inertial relief, they come under rt click study properties
What kind of study you want to calculate? What types of elements are you using (Beams, Shells, Volumes) ?
Sometimes special things have to be kept in mind defining restraints.
Can you share data to have a look on it?
Retrieving data ...