NEGATIVE PIVOT ERROR

I'm currently working on a single-cell box girder (balanced cantilever). The bridge is on a curve and comprises 10 spans. I've modelled the superstructure and piers together and defined the bearings as springs in the pier definition in the modeller.

At the abutment the bridge sits on 2 bearings - free on the outer and fixed on inner side of the curve.
At the pier the bridge sits on 2 bearings - free on the outer and longitudinally free (transversely fixed) on inner side of the curve.
All bearings are free to rotate about all three axes

I've modelled the bearings as described, but I keep getting the negative pivot error. I've tried multiple iterations, including fixing all rotations at all piers, but I get the same error.

Does anybody know what I may be doing wrong here?