tina convergence issue
A convergence error means you have positive feedback in your system and it 'goes to infinity' or your system is as such that it is hard to find the steady state conditions.

It looks like you need a ground.

Another way to combat convergence problems in simulations (not just tina) is to:
1) Introduce parasitic series resistance (kind of like a wire under 1 ohm usually)
2) Introduce parasitic parallel resistance (1e9 Ohms will help some nodes converge, and will have little effect on most circuits)
3) Parasitic capacitance to ground (1e-14 F will knock out some high frequency  numerical errors that may cause the simulation to 'blow up')