I've fallen and I can't get up

[okidoki]

For the past 4 hours haven't been able to access my site or /admin. I keep getting the following message:
Fatal error: Incompatible file format: The encoded file has format major ID 1, whereas the Loader expects 4 in /home/okidoki/public_html/admin/index.php on line 0

Anybody, any clue??

Thanks in advance - - - x10 ROCKS