The closed position is set with a microswitch on the motor, the full open and tilt up are by slipping clutch.
First thing is to check the alignment marks on the roof - there is a single tirangle or punch mark on the slide and a pair of marks on the rail on the drivers side, rear of center. The single mark must be between the two marks on the rail.
I suspect you don't have the roof panel far enough forward and it sticks on the rear edge. I had to "cheat" mine back a little, as I don't have the special tool that fits into the mirror mount hole and the panel -- its a modified ViseGrips thing -- that pulls the roof panel forward into the seal. What I did was to move the panel back not quite an eighth inch with the manual crank and then hold the panel forward by hand while tightening the side bolts. Big PITA, you may have to try several times. If the panel sticks and pops up with a thump, it's still back too far. It may drag enough to make the motor slip.
If this is not the problem, procede to the motor adjsutment.
I'll have to dig up the instructions off the CD, but if I remember correctly, what you do is close the roof properly, if necessary, with the manual crank. Pull off the white plastic nut, then loosen the nut on the manual crank shaft, then turn the shaft with a screwdriver until you can insert a 3mm allen in the reference hole (down and to the left of the manual crank shaft). Tighten lock nut and replace white drive nut.
Please do not operate the motor, manually or otherwise, with the 3mm allen in the hole.....
Test the roof. Should work properly after adjustment.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!