I have been having problems with a simulation ending with the "Timestep too small" error. Looking the error up I came across this document here. As I am using Multisim version 12, I understand the Convergence Assistant tries to solve the error by changing simulation parameters just like you used to have manually in earlier version. As this didn't work, I changed the parameters manually as described but I still get the same error.
I have the circuit and the error report attached to this post.
To resolve convergeence issues, try not to modify the default simulation settings. The following can result in convergence issues; floating components, tiny resistors, direct voltage sources across P-N junctions, and parallel voltage sources and inductors. You can adjust the simulation settings in the Interactive Simulation Settings window (Simulate»Interactive Simulation Settings»Analysis options). Select Use custom settings and select Customize. You can try adjusting the tolerances, by following the guidelines below:
Increase RELTOL to no greater than 0.01
Increase VNTOL to no greater than 1e-3
Increase ABSTOL to no greater than 1e-6
Try switching integration order to Gear, especially when simulation power circuits
Hope this helps.
Sharanya R Market Development Engineer National Instruments