I tried to run a overgrow spell on a Magic Processing unit but it only tells me that my cads stats are too weak even if i use a creative cad i cannot get it to work and i can´t find a tutorial that could show me if i´m missing something.

When running spells on MPUs the MPU itself is the CAD and provides its own set of stats. This is because MPUs are designed to work without needing a player. You can see these stats on the wiki.
MPUs are currently limited to 80 potency. One reason for this is I wanted to prevent automatic Trick: Smite as it felt a bit too powerful especially as you can supply MPUs with much more psi than players could regenerate.
Unfortunately, I haven't realized overgrow has the same potency and it ended up being unusable on MPUs with the current stats. Until I get to adding more powerful MPUs to the mod you can stick to vanilla methods or use other mods for this purpose.