How to block checkout on cart errors?

[picaye]

hi,

i would like to block users from going into the checkout process if they have errors in their cart. example: i use linda's enhandcemnets and have products with minimum order quantity: 3. if someone orders 4 the system recognizes this, but still allows them to checkout...

 

anyone here who knows which part of the code that could be ???

 

thanks

pino