We installed Umbraco 7 and then tried installing uCommerce. For that we downloaded developer version of uCommerce. The filename is "uCommerce-for-Umbraco7-6.0.3.14141". We were installing this as local package.

When we tried first time it said "error occurred. see server logs". When we looked into event viewer, the error was 

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Exception information: 

    Exception type: ConfigurationErrorsException 

    Exception message: Could not load file or assembly 'Castle.Windsor, Version=3.2.0.0, Culture=neutral, PublicKeyToken=407dd0808d44fbdc' or one of its dependencies. The system cannot find the file specified. (C:\inetpub\wwwroot\Umbraco\web.config line 196)

   at System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective)

   at System.Web.Configuration.AssemblyInfo.get_AssemblyInternal()

   at System.Web.Compilation.BuildManager.GetReferencedAssemblies(CompilationSection compConfig)

   at System.Web.Compilation.BuildManager.CallPreStartInitMethods(String preStartInitListPath, Boolean& isRefAssemblyLoaded)

   at System.Web.Compilation.BuildManager.ExecutePreAppStart()

   at System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters, PolicyLevel policyLevel, Exception appDomainCreationException)