Someone mentioned in a recent thread that Windows XP with SP3 will cause timestep errors in Multisim.

Right now, I'd suggest your best bet would be to post an image of your circuit, preferably in .PNG format (compact image file type, not "lossy" like .jpg files, and require no other software than a browser to view)

 

Convergence problems happen in any Spice simulation.

True, but in LTSpice somehow much more often than in others. I guess it cheats somewhere just to be faster than the other simulators and doesn't do its math properly. Good simulators use some heuristics like NR damping for improving the convergence range - but these heuristics cost some CPU clocks to apply.