It could be a million things (well, a few anyway) so it's not clear cut answer.
Is it just one position, or all of them ?
Main pointers is axis configuration, coordinate systems / baseframe setup and TCP (tooldata).
When you say the simulation works well, have you checked how close you are to the limit on that position in the simulation ?
Is the simulation done in RS4 or RS 5/6 ? It might be that newer 140's have a ever so lightly bigger working envelope.
Even if the robot doesn't like a position you can kind of "force it" to go as far as it can by highlighting the position on the TeachPendant and then select "Go To Position" (something tells me it was Special-7, but I haven't touched an S4 pendant in 10 years so I might be wrong)
Once it reaches it's physical limitation you can compare your position data in the jogging window to your data in the robtarget to see where it's different (where you're the most off) and try and figure it out from there.