I assume it's okay to label power supplies as a negative voltage, at the positive end of the icon?
2.
The power supplies to U1 appear to have the negative on top and the positive underneath. Is this permitted?
3.
If the above items are okay, then about all you can try is to
simplify the circuit. Delete a stage (op amp). Watch to see whether the errors stop. Then you'll know which stage is generating errors.