Counting values in Multiple ComboBox's

Hello,

I'm looking for some assistance with excel VBA, it would be great to gain your assistance.

I've created a UserForm with 4 x ComboBox's, each with the same list of values.

I'd like to use a function similar to 'CountIf' for the values selected from the drop box, and if greater than or equal to x, then pop an error msg, and reset to "null"

Thanking you in advance

BJ