There is a new version (188.8.131.521) of MVT available which McAfee recommends should be run to fix the script errors, failure to initialise programs, and connectivity problems caused by the release of DAT 6807 and DAT 6808.
This updated MVT can be downloaded from the link given in this document.
Before you start MVT running, close all other applications. Everything, to be on the safe side. When I ran it, several open applications began spawning multiple copies of active windows. I don't know why it happened, but it's never happened before so there must be some system-level actions that MVT takes which caused them to be created.
When MVT is run, it may immediately switch off the McAfee firewall (it did when I ran it). It may also disable the On-Access Scanner, otherwise known as mcshield. This is what it's supposed to do, so don't panic. You will of course then get the Your System Is At Risk pop-up from McAfee, and possibly (depending on your settings) a notification from Windows Security Center to the effect that there is no firewall currently operating. You should resist the urge to call up McAfee's Security Center to switch the firewall back on.
Let MVT run its course. Wait for the report stage, and look through the errors and missing/corrupted/outdated components it says it finds. Take that first report with a very large pinch of salt; it's only an interim report. Let MVT attempt to fix the problems it says it's found. It will then probably demand a re-boot (and may quite possibly do it straight away, which is another reason not to have other programs open at this stage; you might not have time to close them yourself before MVT does it for you).
If a restart was required, log back in, and MVT will automatically restart when you log on. Check the report section again. If it still shows errors (and it did for me) run it again. A second pass is apparently needed for many systems. After the second pass everything should be fixed, and you get the green tick on the MVT screen. At this stage, if your McAfee firewall is still switched off, call up the Security Center and manually switch it on.
I don't guarantee that MVT will fix every single system that's been having problems caused by that faulty DAT, but feedback is that it fixes more than 80% of them without needing to uninstall McAfee and re-install it. It's quicker, too.
Not everyone will need to run MVT twice; not everyone will see the reported errors I saw (iDispatch was one of them); not all systems will have their firewall switched off or mcshield disabled. The faulty DAT caused all sorts of errors on different systems, which is in part why sorting it out has been such a prolonged affair.