Your description is a little hard to follow. Either you have a scripting engine or you're using vb scripting to check something.
Those are the only entities that process code in strings, unless I don't understand you.

Whether it's walls or not doesn't matter too much.

Can you be more explicit - what error and what are you doing?

There are essentially no limits to vb string size. Some scripting engines choke on long strings. Vb doesn't choke on long strings unless you're concatenating really big ones over & over.