I lost a few nights' sleep over an issue about 4 years ago, before I finally stood up to my boss and told him I wasn't qualified for the work he had me struggling with. He had nearly a hundred detailed blueprints of various automotive parts and he wanted me to take the information from them and add it all to a database.
I tried doing this for a while, but was not getting anywhere. I kept having to leave blanks where I couldn't understand certain details. Then I'd have to interrupt my boss to figure these out when he had time. Sometimes I'd put information in that turned out to be wrong. It was all very stressful.
He actually understood completely when I explained this assignment wasn't going to work out. It helped that an engineering associate pointed out that I should be given more administrative work, not engineering detail work (when he was discussing another matter with him).
Mind you, I wouldn't mind being responsible for such difficult, tedious work, if I was trained and properly compensated for it.
Movinonup 
