Runtime Error with MS Access 2000 Runtime not with Full Version

The AfterUpdate event of a TextBox causes MS Access 2000 Runtime to crash, but running the same database from MS Access 2000 full version does not.

The AfterUpdate event contains the following code;

Private Sub TenderDue_AfterUpdate()
Dim SearchString, SearchChar As String
Dim Mypos, MyNumber As Integer

' Tender Valid is a combo box value list
' First 2 or 3 digits are a number
SearchString = Me.[TendValid]
' Set Variable to Space
SearchChar = " "
' Set Design Due date to Tender due date less 7 days
Me.[Design_Due] = Me.[TenderDue] - 7
'Locate position of space in Tender Valid
Mypos = InStr(1, SearchString, SearchChar, vbTextCompare)
'Extract Number from String
MyNumber = Mid(SearchString, 1, Mypos - 1)
' Set Date of Validity to Tender Due + number of Days
Me.[ValidDate] = Me.[TenderDue] + MyNumber

End Sub

It would appear that at the time the Runtime User triggered the AfterUpdate event the Design_Due control was locked. This seems to be ignored by the Full Version but causes the Runtime version to crash. If anyone can confirm this of course.


Regards
Peter