Rc1 + w2k/iis5 + session_start =>exception

I'm running RC1 on Windows 2000 pro/iis5. I'm getting the following in the system eventlog when using a session_start in a page. My session save path is as follows: session.save_path = d:\inetpub\wwwroot\session There are 0 byte files in this director, one for each load on the page that begins with <? session_start(); ?> =============== The HTTP server encountered an unhandled exception while processing the ISAPI Application ' php4isapi!HttpExtensionProc + 0x394 wam!STR::STR(char const *) + 0x239 wam!DllGetClassObject + 0x808 w3svc!_WamDictatorDumpInfo@8 + 0x2DB w3svc!HTTP_REQUEST::GetInfo(char const *,class STR *,int *) + 0xD61 w3svc!HTTP_REQUEST::GetInfo(char const *,class STR *,int *) + 0xC39 w3svc!HTTP_REQUEST::GetInfo(char const *,class STR *,int *) + 0xBA1 w3svc!HTTP_HEADERS::FindValue(char const *,unsigned long *) + 0x58B w3svc!HTTP_HEADERS::FindValue(char const *,unsigned long *) + 0x2D5 w3svc!ADDRESS_CHECK::UnbindAddr(void) + 0x175 w3svc!ADDRESS_CHECK::UnbindAddr(void) + 0xEF ISATQ!_AtqSpudInitialized@0 + 0x20F ISATQ!CDirMonitor::EqualKeys(char const *,char const *) + 0x129 + 0x5286636F '. For additional information specific to this message please visit the Microsoft Online Support site located at: http://www.microsoft.com/contentredirect.asp.