Go into the Menu/Settings/PC Control. Select any Baud rate or speed other than Off and Remote mode should be enabled. Set ARC250 to the same Baud rate you selected.
At first I thought the 296 was like the 780XLT where you held down the E key which toggle RMT on or off in the radio's display but that seems to not be the case for the 296. I found the above info in the 296 owner's manual on page 61. They call it PC Control Mode but it's the same thing.
Set the fastest speed 57600 bps on both your scanner and software. I assume that you have the nonstandard cable for programming it. The latest firmware for the 296 is v3_60.scn.