Application deployment - 20% return 'unknown'

I've deployed a package which is a vbscript out to 700 clients to change their dns/wins settings. 80% return a success but 20% return 'unknown'. I've connected to a few manually to see what's going on but there's no entry in execmgr.log so it looks like it doesn't reach this stage. What's the stage/log before it hits this that i should check?

Thanks