Update a date field to NULL

Hi
I'm not sure if I'm going about this the right way.  I'm trying to update a table with values from a form.  The problem I am having is that sometimes these values are empty, and sometimes they have data.  I've got round this by using IIF functions in my update statement, however this isn't quite working on a date field.  Basically the date may be blank, in which case it should update the datetime field in the table to null, or it may have a date value (running the update in this instance works).  I'm getting type conversion errors when I try to update to null.  Code attached, many thanks
"dbo_tbl_Weekly_Expenses_Temp.[LaundryLetters1] = IIf(IsNull('" & LaundryLetters1 & "'),'', '" & LaundryLetters1 & "'), " & _ 'This line works fine, updating a text field
         "dbo_tbl_Weekly_Expenses_Temp.[LaundryLetters1Date] = IIf(IsNull('" & LaundryLetters1Date & "'),'', '" & LaundryLetters1Date & "') " & _ 'This line errors, updating datetime field

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grunners80Asked:
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Gustav BrockConnect With a Mentor CIOCommented:
A right paranthesis was missing:

 "dbo_tbl_Weekly_Expenses_Temp.[LaundryLetters1Date] = " & IIf(IsNull(LaundryLetters1Date), Null, Format(LaundryLetters1Date, "\#yyyy\/mm\/dd\#")) & ""

And
dbo_tbl_Weekly_Expenses_Temp.[LaundryLetters1Date]
is of DateTime data type?

/gustav
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Guy Hengel [angelIII / a3]Billing EngineerCommented:
change:

IIf(IsNull('" & LaundryLetters1Date & "'),'', '" & LaundryLetters1Date & "')
into:
IIf(IsNull('" & LaundryLetters1Date & "'), NULL, '" & LaundryLetters1Date & "')
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grunners80Author Commented:
Thanks, I'd tried that earlier, Access errors

"...Access didn't update 3 field(s) due to a type conversion failure"

I know though that if I put a date in and leave the other 2 fields as null the update goes through fine, so it's definitely the date that is causing the problem.

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Guy Hengel [angelIII / a3]Billing EngineerCommented:
ok, let's go 1 step further:
 " & IIf(IsNull(LaundryLetters1Date), "NULL", "#" & LaundryLetters1Date & "#") & " 

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Mr_BenCommented:
Try:

IIf(IsNull('" & LaundryLetters1Date & "'),'', '" & LaundryLetters1Date & "')
into:
IIf(IsNull('" & LaundryLetters1Date & "')," & # NULL# & ", '" & LaundryLetters1Date & "')
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grunners80Author Commented:
I've managed to get it to work with the following, however if the condition is false it now won't update the date with that in the text box!  
IIf(Nz([forms]![frm_Expenses]![txtLaundryDate1])=0, Null, '" & LaundryLetters1Date & "')

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grunners80Author Commented:
My question is, how can i still be getting a data type mismatch error when trying to update using the EXACT same code in an IIF statement that I use as simple criteria in an update?
'For instance, this works:
 
"dbo_tbl_Weekly_Expenses_Temp.[LaundryLetters1Date] ='" & Format([Forms]![frm_Expenses]![txtLaundryDate1], "yyyy-mm-dd") & "'" & _
 
'But this doesn't:
 
"dbo_tbl_Weekly_Expenses_Temp.[LaundryLetters1Date] = IIf(Nz([forms]![frm_Expenses]![txtLaundryDate1])=0, Null, '" & Format([Forms]![frm_Expenses]![txtLaundryDate1], "yyyy-mm-dd") & "') " & _

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Gustav BrockCIOCommented:
You are making it too complicated:

  "dbo_tbl_Weekly_Expenses_Temp.[LaundryLetters1Date] = " & IIf(IsNull(LaundryLetters1Date, Null, Format(LaundryLetters1Date, "\#yyyy\/mm\/dd\#")) & ""

/gustav
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grunners80Author Commented:
Datatype mismatch in criteria expression again.  This is really bugging me now, it's a day ruiner!
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