TwoHandedSword: MSR is your Minimum Strength Required to wield that weapon without additional penalties.
Weapons which can be used either one- or two-handed (the bigger swords, axes, hammers, etc.) have a higher strength requirement when being swung with just one hand. (If you don't put anything in the shield slot, the game assumes you're using both hands.)
Using a too-heavy weapon increases your chances of a critical miss, based on how wide the strength difference is.
What TA (tech aptitude) affects is the magical bonus from weapons and armour. If a certain item has a MA of 40, for example, you'd need at least that much MA to gain the full bonus, and if you had at least that much TA you'd lose any extra benefit. (In between, the item's magickal bonus is proportional to how close you come to either extreme.)
Thanks for the replies, I see now that if I unequip the shield the penalty is removed.