Try going into the Umbraco developer section and saving one of the XSLT files.

This should give you some kind of useful exception message which you can then paste here.

System.Exception: Unable to load one or more of the types in assembly 'Recaptcha, Version=1.0.5.0, Culture=neutral, PublicKeyToken=9afc4d65b28c38c2'. Exceptions were thrown:
System.IO.FileNotFoundException: Could not load file or assembly 'System.Web.Mvc, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified. 
at umbraco.BusinessLogic.Utils.TypeFinder.FindClassesMarkedWithAttribute(Assembly assembly, Type attribute) 
at umbraco.BusinessLogic.Utils.TypeFinder.FindClassesMarkedWithAttribute(Type attribute) 
at umbraco.macro.GetXsltExtensionsImpl() 
at umbraco.macro.b__4() 
at umbraco.cms.businesslogic.cache.Cache.GetCacheItem[TT](String cacheKey, Object syncLock, CacheItemPriority priority, CacheItemRemovedCallback refreshAction, CacheDependency cacheDependency, TimeSpan timeout, GetCacheItemDelegate`1 getCacheItem) 
at umbraco.macro.GetXsltExtensions() 
at umbraco.macro.AddMacroXsltExtensions() 

Do you have asp.net MVC installed?

i found this: http://stackoverflow.com/questions/4499405/add-reference-to-dll-asp-net which suggests its the wrong version of the dll, this guy said he used and older version and it worked, but there only seems to be one version on the recaptcha site

I dont think so, this is not an mvc project and i havent touched mvc before. where do i install it? will it affect anything on the site if i do?

You can download the runtime from http://www.asp.net/mvc

After installation you can find the installed DLL's on C:\Program Files (x86)\Microsoft ASP.NET

Then just copy the DLL into the bin folder.

THANKS ERAN! this has caused me so much stress, i havent been able to find a solution anywhere.

I had this issue after upgrading a site (which included a user control using reCaptcha) from 4.5.2 to 4.7.1, and was very glad to see that other users had already posted on it - thanks guys !    I tried Eran's solution above, which unfortunately didn't work in this case.  So I tried some of the other advice and downgraded the reCaptcha dll from 1.05 to 1.03 (obviously I also had to recompile the user control) - this fixed the problem for me.

Okey Dokey,

I hit this error on .net 4 running Umbraco 4.7.1.1.

This is the full runtime node so you can get a bit more context but I only had to add the last dependentAssembly node and it was fixed.

  <runtime>
    <!-- Old asp.net ajax assembly bindings -->
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <dependentAssembly>
        <assemblyIdentity name="System.Web.Extensions" publicKeyToken="31bf3856ad364e35" />
        <bindingRedirect oldVersion="1.0.0.0-1.1.0.0" newVersion="4.0.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="System.Web.Extensions.Design" publicKeyToken="31bf3856ad364e35" />
        <bindingRedirect oldVersion="1.0.0.0-1.1.0.0" newVersion="4.0.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="System.Web.Mvc" publicKeyToken="31bf3856ad364e35"/>
        <bindingRedirect oldVersion="1.0.0.0" newVersion="3.0.0.0"/>
      </dependentAssembly>
    </assemblyBinding>
  </runtime>

Cheers

None of this worked for me so another option is download the recaptcha source via SVN...

http://code.google.com/p/recaptcha/source/checkout

...then remove the references to MVC & the MVC Control, recompile, and done!

@Olie, did you get your non mvc working? I downloaded, took out the mvc references n recompiled, but doesn't want to work.

pete

Eran and Ben's solutions should work - the key thing is newVersion of the DLL you are mapping to must match the one you actually have :o)

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