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Asked: 2026-05-24T03:42:36+00:00

I’ve inherited an asp.net 3.5 solution and I’m having trouble getting it working. I

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I’ve inherited an asp.net 3.5 solution and I’m having trouble getting it working. I keep receiving the error:

Could not load file or assembly ‘Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35’ or one of its dependencies. The system cannot find the file specified. (c:\mydir\web.config line 54)

Now, I’ve had a good look around Google and have seen that people have said to run a simple search and replace to change “Microsoft.Web.” to “System.Web.” as the namespaces have changed, but I’m having no luck at all.

These are the pertinent lines of the Web.config file

<pages validateRequest="True">
    <controls>
        <add tagPrefix="asp" namespace="Microsoft.Web.UI" assembly="Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
            <add tagPrefix="asp" namespace="Microsoft.Web.UI.Controls" assembly="Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
    </controls>
    <tagMapping>
        Line 54: <add tagType="System.Web.UI.WebControls.CompareValidator" mappedTagType="Microsoft.Web.UI.Compatibility.CompareValidator, Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
        <add tagType="System.Web.UI.WebControls.CustomValidator" mappedTagType="Microsoft.Web.UI.Compatibility.CustomValidator, Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
        <add tagType="System.Web.UI.WebControls.RangeValidator" mappedTagType="Microsoft.Web.UI.Compatibility.RangeValidator, Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
        <add tagType="System.Web.UI.WebControls.RegularExpressionValidator" mappedTagType="Microsoft.Web.UI.Compatibility.RegularExpressionValidator, Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
        <add tagType="System.Web.UI.WebControls.RequiredFieldValidator" mappedTagType="Microsoft.Web.UI.Compatibility.RequiredFieldValidator, Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
        <add tagType="System.Web.UI.WebControls.ValidationSummary" mappedTagType="Microsoft.Web.UI.Compatibility.ValidationSummary, Microsoft.Web.Extensions, Version=1.0.61025.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"/>
    </tagMapping>
</pages>

I would appreciate any insight into this, as I’m really struggling.

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1 Answer

  1. Editorial Team

    As it turns out, I had been given an incorrect web.config by the previous developers. Putting the new one in allowed me to compile and build the solution.

    Once deployed to the server, I had installed the AJAX for ASP.NET 2.0, but still received errors referencing microsoft.web.extensions etc.

    The solution lie in the versioning.

    The whole application seems to be built on top of the AJAX for ASP.NET Beta 2 binary. After removing the 2.0 and re-installing the beta 2 MSI, everything fired into action.

    Thanks for the pointers everyone.

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