Can you post your cap? Easier to help that way.
I tried something similar with Custom Movement and got something working pretty sweet, though in the end I've opted to go for the 8 directional movement behavior.
The way I prevented the player from going through solids was by doing
If Player Overlaps Solid
--> Push Player out of Solid, Normal
Gives mostly wonderful results. The push out of object action is a custom movement action that you can find near the bottom.