Answer:
A calculation break‑off due to an unstable system can have different reasons. There can be a "real" instability due to an overload of the system, but instability effects can also occur due to failing members.
In the calculation parameters, you can deactivate the "Members due to member type" nonlinearity (see Image 01). If the calculation is then possible without the error message, the problem is probably caused by failing members.
Complete failure of the tension members can be prevented using the option "Failing Members to be Removed Individually During Successive Iterations" in the dialog box Global Calculation Parameters (see Image 02). This should help in most cases. The number of possible iterations should be specified as sufficiently large.
An alternative method is to apply a prestress to the tension members to prevent them from failing.