This is the second time I have encountered this now. Both sites were completely unrelated and had different IT admins. In each case, for whatever reason EAS was not working, probably due to SSL problem or IP address restrictions, but in trying to fix the problem, the IT person left the machine with ExchangeVdir set to /exchange-oma, but no such virtual directory in IIS.
To fix, I simply removed the ExchangeVdir registry entry, but according to MS KB article 817379, on SBS 2003 the key should indeed be set, and a virtual directory should exist called exchange-oma. Therefore, it seems that the IT person is doing the re-build of Exchange IIS virtual directories (as per the well known MS KB article where you do the metabase edit), but the re-build does not create the SBS-only non-standard exchange-oma directory. I am guessing that the CEICW recreates the exchange-oma virtual directory, otherwise it must be manually created as per kb817379.
In any case, this is something to look for when EAS does not work. The IIS logfiles show the requests for /exchange-oma, which does not exist.
The key issue here is that in attempting to fix a problem, the IT person compounds the problem with exactly the same symptoms but a totally different cause. They probably then move on and fix the initial cause of the problem, but it still doesn’t work because they just goofed up the ExchangeVdir stuff.