Issue with adding Excel COM reference in VS 2005 using Office 2003

I have an application that was created using office 2003 and the Microsoft.Office.Interop.Excel.dll.  Everything has worked great for a year or so with the portion of the app that writes to Excel.  My pc was recently upgraded to Office I had to remove the old and add the new references for issues.  The problem was though, the app runs from Citrix, and since it has Office 2003, I needed to change them worries right?

Well, I made the changes on a pc with Office 2003, ran the app locally...everything worked.  Placed the app on the server and the Excel portion blows up.  It appears that when I added the Office 2K3 reference back in, it is now using Interop.Excel.dll...a different dll then what it was using before.

Now, I can just replace that other dll with the one it is currently using, but I want to know why it is using Interop.Excel.dll as opposed to Microsoft.Office.Interop.Excel.  I have tried this on a few pc's with Office 2K3 and I get the same result.
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HairbrushConnect With a Mentor Commented:
Microsoft.Office.Interop.Excel.dll is a "Primary Interop Assembly" (PIA) which is the "official" interop assembly as distributed by Microsoft.  It is strongly named and installed in the GAC. The intention is that this assembly is used by all applications that need to call the Excel API.  (IF you have multiple versions of Office then you may have more than one Microsoft.Office.Interop.Excel.dll in your GAC as they will have different signatures - the version number will be different)

Your Interop.Excel.dll sounds like it has been generated by creating a reference directly to the Excel.exe COM object.  Microsoft recommends against referencing the Office applications in this way.  See the third article below.

Sounds like you do not have the Office 2003 PIAs on the server.  You can check by looking in the GAC.

Hope this helps.
Éric MoreauSenior .Net ConsultantCommented:
because you are targeting a different version, you have 2 options here:
-switch to late binding (do not add a reference and use GetObject to create your instance)
-use a 3rd party application like
rgn2121Author Commented:
I am targeting Office 2003...only Office 2003.  The last time I add the reference it used Microsoft.Office.Interop.Excel.dll.  Now it uses Interop.Excel.dll...both for Office 2K3 (Office 11)
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Éric MoreauSenior .Net ConsultantCommented:
you are targeting Office 2003 but you have something different installed on your PC!
rgn2121Author Commented:
I have 2K3 on the PC's that I am developing on today...I have tried 2 office 2k3 pc's as stated above...
rgn2121Author Commented:
Thanks Hairbrush...I was adding my references the way link 3 described, but it kept choosing the Interop.Excel.dll.  One pc had the Office 2003 PIA's installed the other did not.  I installed them on the pc that needed them and it selected the correct dll.  I found out that from another developer in my dept that he has to do this almost every time there is an office update...I just didn't know it since it had been so long since I have been in this application.

Thanks for the links...
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