You might want to remove the crank arm and inspect the tapers. Check the bottom bracket axle tapers as well. If there is a lot of corrosion or dirt you might use a fine brass brush and some wd40 to clean things up a bit. Then wipe with clean paper towels. You could rotate the crank on the tapers just to try a slightly different position. Then reinstall. Reserve your torque wrench for final tightening. I would recommend a longer ratchet, a "T" wrench or a medium breaker bar. Something that will give you tactile feedback that the crank arm is tightening onto the tapers of the bottom bracket axle correctly. The "T" wrench is ideal for this since you can apply more balanced force to overcome any resistance. Just don't go crazy. Don't grease the tapers of the bottom bracket axle but you can apply a little bit of grease to the bolt threads, the washer and the socket inside the crank arm where the washer rests. This will keep that part of the system well lubed and easy to disassemble later. It will also permit more seamless tightening of your crank arm as you approach the torque figure you provided. Not sure what type of torque wrench you are using but 250 inch pounds is at the top limit of a 1/4" torque wrench. You might do better do use a conversion into foot pounds and use a longer 1/2 drive torque wrench.