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Steve, 
 
&lt;&lt;note: at this point for so many instances, you should have learned this syntax already.&gt;&gt; 
 
&nbsp;I'm sorry, but I have to say I would second that. &nbsp;You've been asking this same question over and over for some time now. &nbsp; 
 
&nbsp;We have pointed out what your doing wrong, and also have suggested many times now that you do it this way: 
 
&nbsp;Dim strWhere as string 
 
strWhere = &quot;[AppliedToOpenOrdRecID] = &quot;&nbsp;&amp; Me!txtOpenOrderRecID 
Me.txtInventoryAppliedQty = Nz(DSum(&quot;[Quantity Out]&quot;, &quot;tblInventoryDetail&quot;,strWhere), 0) 
 
which your still not doing. 
 
Doing this allows you to put a break point or a stop in place and inspect strWhere to see exactly what the statement sees when it executes if your having a problem. 
 
If you do this, it will help a lot and in that you'll be able to see where your mistake is. &nbsp;Please start doing this. 
 
Also please read: 
 
<a href="https://www.experts-exchange.com/articles/12/Dlookup-and-the-Domain-Functions.html" rel="ugc">https://www.experts-exchange.com/articles/12/Dlookup-and-the-Domain-Functions.html</a> 
 
about half way down, that article deals with putting things inside a string (which is what the WHERE argument is), including other strings. 
 
While we want to help in every way possible, most of us like to see some effort on your part in trying to learn what you have been having a problem with. 
 
Thanks, 
Jim.
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What is wrong with this: &nbsp;(used on a form. &nbsp;And AppliedToOpenOrdRecID and txtOpenOrderRecID are both numeric values) 
 
Me.txtInventoryAppliedQty = Nz(DSum(&quot;[Quantity Out]&quot;, &quot;tblInventoryDetail&quot;, &quot;[AppliedToOpenOrdRecID] = Me!txtOpenOrderRecID, 0)
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What is wrong with this:  (used on a form.  And AppliedToOpenOrdRecID and txtOpenOrderRecID are both numeric values)

Me.txtInventoryAppliedQty = Nz(DSum("[Quantity Out]", "tblInventoryDetail", "[AppliedToOpenOrdRecID] = Me!txtOpenOrderRecID, 0)

DSum syntax issue

Microsoft Access is a rapid application development (RAD) relational database tool. Access can be used for both desktop and web-based applications, and uses VBA (Visual Basic for Applications) as its coding language.