Windows Form Designer: Could not load file or assembly

Admin 1
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Has anyone ever had the issue where trying to "View Designer" on a windows form in Visual Studio .NET causes the error: "Could not load file or assembly…" ?

In this case, the assembly in question was XYZ.dll. I managed to fix this by adding XYZ.dll and all its references to my project's references (even though my project doesn't directly depend on them) and rebuilding the whole solution. However, after that, I removed all those references from my project, rebuilt, and it still worked.

One other piece of information is that I use Resharper 2.5. Someone else pointed out that it might be Resharper doing some shadow copying. I'll look into this next time this happens. Does anyone have a understanding of why this error happens in the first place, and possibly the 'correct' way to fix it?

windows-forms-designer visual-studio
22 Answers

We have same problem. Some Form/UserControl classes can not be viewed in designer and Visual Studio causes various exceptions.

There are one typical cause: One of designed component thrown unhandled exception during initialization ( in constructor or in Load event or before ).

Not only for this case, you can run another instance of visual studio, open/create some independent project, go to menu -> Debug -> Attach to process ... -> select instance of devenv.exe process with problematic designer. Then press Ctrl+Alt+E, the "Exceptions" windows should be shown. There check "Thrown" in categories of exception.

Now active the visual studio with designer and try view designer. If the exception will be thrown, you will see callstack ( and maybe source code, if the exception was thrown from your code ) and other typical information about thrown exception. This information may be very helpful.

user_203820

Using VS 2005, I ran into this same problem. I performed the steps Chien listed in his original question, but it still didn't work until I closed VS and reopened the solution. Now the Designer view looks fine.

Dean_Hill_31060

It happened to me very frequently on VS2005, specially when adding custom controls to the winform. Usually I just needed to just rebuild, without needing to add extra references, or close and reopen VS.

There is no apparent cause for this, just VS bugs.

Santiago_Palladino_127910

I concur with the Resharper comment. I'm running 4.1. I disabled it, restart VS2008, and tried the "Convert to Web Application" again, and it worked.

Admin1

Just to Chime in on this. I build a new version of my UserControl whilst my other project was open and referencing it. When I went back to view the designer in the form referencing the user control, it said it couldn't find the .dll of a specific version.

I tried to remove the reference to the control and from the toolbox, with no luck. The code would compile just fine, but the designer wouldn't show without the error.

Tried all the above and it didn't work.

The .res file for the form has some XML:

<data name="EventBar1.EventCheckedSubscriptions" mimetype="application/x-microsoft.net.object.binary.base64">
    <value>
        AAEAAAD/////AQAAAAAAAAAMAgAAAJoBbXNjb3JsaWIsIFZlcnNpb249NC4wLjAuMCwgQ3VsdHVyZT1u
        ZXV0cmFsLCBQdWJsaWNLZXlUb2tlbj1iNzdhNWM1NjE5MzRlMDg5XV0sIG1zY29ybGliLCBWZXJzaW9u
        PTQuMC4wLjAsIEN1bHR1cmU9bmV1dHJhbCwgUHVibGljS2V5VG9rZW49Yjc3YTVjNTYxOTM0ZTA4OQUB
        AAAANlN5c3RlbS5Db2xsZWN0aW9ucy5HZW5lcmljLkxpc3RgMVtbU3lzdGVtLkV2ZW50SGFuZGxlcgMA
        AAAGX2l0ZW1zBV9zaXplCF92ZXJzaW9uAwAAFVN5c3RlbS5FdmVudEhhbmRsZXJbXQgIAgAAAAkDAAAA
        AAAAAAAAAAAHAwAAAAABAAAAAAAAAAMTU3lzdGVtLkV2ZW50SGFuZGxlcgs=
</value>
  </data>
  <data name="EventBar1.EventLengthSubscriptions" mimetype="application/x-microsoft.net.object.binary.base64">
    <value>
        AAEAAAD/////AQAAAAAAAAAMAgAAAJoBbXNjb3JsaWIsIFZlcnNpb249NC4wLjAuMCwgQ3VsdHVyZT1u
        ZXV0cmFsLCBQdWJsaWNLZXlUb2tlbj1iNzdhNWM1NjE5MzRlMDg5XV0sIG1zY29ybGliLCBWZXJzaW9u
        PTQuMC4wLjAsIEN1bHR1cmU9bmV1dHJhbCwgUHVibGljS2V5VG9rZW49Yjc3YTVjNTYxOTM0ZTA4OQUB
        AAAANlN5c3RlbS5Db2xsZWN0aW9ucy5HZW5lcmljLkxpc3RgMVtbU3lzdGVtLkV2ZW50SGFuZGxlcgMA
        AAAGX2l0ZW1zBV9zaXplCF92ZXJzaW9uAwAAFVN5c3RlbS5FdmVudEhhbmRsZXJbXQgIAgAAAAkDAAAA
        AAAAAAAAAAAHAwAAAAABAAAAAAAAAAMTU3lzdGVtLkV2ZW50SGFuZGxlcgs=
</value>
  </data>
  <data name="EventBar1.EventLengthTypes" mimetype="application/x-microsoft.net.object.binary.base64">
    <value>
        AAEAAAD/////AQAAAAAAAAAMAgAAAKABY3RybENhbGVuZGFyU2lkZUJhciwgVmVyc2lvbj0xLjAuNzEy
        MS4yMTIzNCwgQ3VsdHVyZT1uZXV0cmFsLCBQdWJsaWNLZXlUb2tlbj1udWxsXV0sIG1zY29ybGliLCBW
        ZXJzaW9uPTQuMC4wLjAsIEN1bHR1cmU9bmV1dHJhbCwgUHVibGljS2V5VG9rZW49Yjc3YTVjNTYxOTM0
        ZTA4OQwDAAAAUWN0cmxDYWxlbmRhclNpZGVCYXIsIFZlcnNpb249MS4wLjcxMjEuMjEyMzQsIEN1bHR1
        cmU9bmV1dHJhbCwgUHVibGljS2V5VG9rZW49bnVsbAUBAAAAT1N5c3RlbS5Db2xsZWN0aW9ucy5HZW5l
        cmljLkxpc3RgMVtbY3RybENhbGVuZGFyU2lkZUJhci5FdmVudEJhcitFdmVudExlbmd0aFR5cGUDAAAA
        Bl9pdGVtcwVfc2l6ZQhfdmVyc2lvbgQAAC5jdHJsQ2FsZW5kYXJTaWRlQmFyLkV2ZW50QmFyK0V2ZW50
        TGVuZ3RoVHlwZVtdAwAAAAgIAgAAAAkEAAAAAAAAAAAAAAAHBAAAAAABAAAAAAAAAAQsY3RybENhbGVu
        ZGFyU2lkZUJhci5FdmVudEJhcitFdmVudExlbmd0aFR5cGUDAAAACw==
</value>
  </data>
  <data name="EventBar1.EventSettingsSubscriptions" mimetype="application/x-microsoft.net.object.binary.base64">
    <value>
        AAEAAAD/////AQAAAAAAAAAMAgAAAJoBbXNjb3JsaWIsIFZlcnNpb249NC4wLjAuMCwgQ3VsdHVyZT1u
        ZXV0cmFsLCBQdWJsaWNLZXlUb2tlbj1iNzdhNWM1NjE5MzRlMDg5XV0sIG1zY29ybGliLCBWZXJzaW9u
        PTQuMC4wLjAsIEN1bHR1cmU9bmV1dHJhbCwgUHVibGljS2V5VG9rZW49Yjc3YTVjNTYxOTM0ZTA4OQUB
        AAAANlN5c3RlbS5Db2xsZWN0aW9ucy5HZW5lcmljLkxpc3RgMVtbU3lzdGVtLkV2ZW50SGFuZGxlcgMA
        AAAGX2l0ZW1zBV9zaXplCF92ZXJzaW9uAwAAFVN5c3RlbS5FdmVudEhhbmRsZXJbXQgIAgAAAAkDAAAA
        AAAAAAAAAAAHAwAAAAABAAAAAAAAAAMTU3lzdGVtLkV2ZW50SGFuZGxlcgs=
</value>
  </data>

I removed this from the .res file and all is well. I did backup the whole folder before I tried this though!

user_105701440
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