They are all the same version (8.1.20081.1000), except for two - Infragistics.Office2007UI.Design.Support.v8.1.dll (v1.0.0.0) and Infragistics.Licence.dll (v1.0.5005.10)

The only other thing I can think of to determine whether or not separate versions are getting loaded is the following:

1. Open two instances of VS2008

2. Open your project in the first instance

3. Open the designer for the form having the problem

4. Minimize this instance of VS2008

5. On the second instance of VS2008, go to Debug > 'Attach to Process...' (or Ctrl+Alt+P by default)

6. Select the instance of VS2008 (the process name is 'devenv.exe') that has your project open

7. In the 'Attach To' box, make sure 'Managed' is one of the comma delimited items. If not, click the 'Select...' button and choose it manually.

8. Click 'Attach'

9. When the dialog closes, go to Debug > Windows > Modules (or Ctrl+D,M by default)

After all the modules are loaded, make sure all Infragistics dlls have the same version. If not, reply with the names of the dlls that differ and I might be able to help determine why they are different.

 Bit more research. I created a new project in VS2008/Infragistics 8.1, and this one works fine. The dropdownbutton works the way it should. So it seems it is just my development project.

I just did a search for 7.3 in my whole solution, and the only occurance was in the app.config file. I removed the following portion, which had no effect (dropdownbuttons still arnt working)

    <runtime>
        <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
            <dependentAssembly>
                <assemblyIdentity name="Infragistics2.Win.UltraWinEditors.v7.3" publicKeyToken="7DD5C3163F2CD0CB" culture="neutral"/>
                <bindingRedirect oldVersion="0.0.0.0-7.3.20073.1041" newVersion="7.3.20073.1041"/>
            </dependentAssembly>
            <dependentAssembly>
                <assemblyIdentity name="Infragistics2.Win.UltraWinGrid.v7.3" publicKeyToken="7DD5C3163F2CD0CB" culture="neutral"/>
                <bindingRedirect oldVersion="0.0.0.0-7.3.20073.1041" newVersion="7.3.20073.1041"/>
            </dependentAssembly>
            <dependentAssembly>
                <assemblyIdentity name="Infragistics2.Shared.v7.3" publicKeyToken="7DD5C3163F2CD0CB" culture="neutral"/>
                <bindingRedirect oldVersion="0.0.0.0-7.3.20073.1041" newVersion="7.3.20073.1041"/>
            </dependentAssembly>
            <dependentAssembly>
                <assemblyIdentity name="Infragistics2.Win.Misc.v7.3" publicKeyToken="7DD5C3163F2CD0CB" culture="neutral"/>
                <bindingRedirect oldVersion="0.0.0.0-7.3.20073.1041" newVersion="7.3.20073.1041"/>
            </dependentAssembly>
            <dependentAssembly>
                <assemblyIdentity name="Infragistics2.Win.v7.3" publicKeyToken="7DD5C3163F2CD0CB" culture="neutral"/>
                <bindingRedirect oldVersion="0.0.0.0-7.3.20073.1041" newVersion="7.3.20073.1041"/>
            </dependentAssembly>
        </assemblyBinding>
    </runtime>

 I checked the infragistics references, and they are all how you said they should  be.

I deleted the contents of licences.licx.

I uninstalled infragistics and reinstalled it.

Still doesnt work.

 I should point out, that it only seems tob e a problem with the UltraDropDownButton. In other scenarios the UltraToolbarManager is working just fine:

1) In another form, I am dynamically generating a context menu - this works as I want it to.

2) On form where I am trying to use the UltraDropDownButton, if I put the code:  ultraToolbarsManager1.ShowPopup("popupMenu"); , it shows the menu that I want to see on the UltraDropDownButton.

Its just the UltraDropDownButton - even though I have the popup menu selected in the  "PopupItem" property.

I did log a bug thingy - but they tell me that it is working fine also. 

I was not able to reproduce the issue on my machine, but it could be a problem caused by a certain machine configuration. 

However, it definately sounds to me like mulitple versions of our product are getting loaded. Another thing to try would be to make sure none of your Infragistics dll references have Copy Local set to True. Set them all to False. Then delete all entries from the licenses.licx file in the project. Also, if any of the Infragistics dll references have Specific Version set to True, make sure they point to the same version number.