Active Script OK But Scheduled Job Fails

I have an ActiveX Script task in a DTS package which executes fine
within DTS.
However, if I run it as a sheduled job, it fails with a 'path not
found error'. I've cut the code down to the approriate problem and
posted it here, it just makes a simple text file with a name derived
from the current date and time and puts 'Hello World' in the file
although in reality I go on to make an xml file. (make sure your path
exists before you execute it). Why does the scheduled job not execute
this simple task. I have loads of other jobs that run packages to a
schedule and the account is a domain account with windows
administrative rights.

'******************************
' Visual Basic ActiveX Script
'**********************

Const strPath="d:xml"

Private Function GetDateTime()
Dim strNow, stryear, strMonth, strDay, strTime
strNow = Now
stryear = Mid(strnow, 7, 4)
strMonth = Mid(strnow, 4, 2)
strDay = Left(strnow, 2)
strTime = Replace(Mid(strnow, 12, 8), ":", "")

GetDateTime = stryear + strMonth + strDay + strTime
End Function

Function Main()
Dim fso,f,MyFile 'file objects
Set fso = CreateObject("Scripting.FileSystemObject")
dim strRightNow
strRightNow=GetDateTime()
Set MyFile= fso.CreateTextFile(strPath &"" & "UPD-"
& strRightNow & ".txt", True) 'This line fails from a scheduled job
MyFile.WriteLine("Hello World")
MyFile.Close
Main = DTSTaskExecResult_Success
End Function

'Error Source= Microsoft VBScript runtime error Error Description:
Path not found Error on Line 25