Could not load file or assembly 'System.Data' or one of its dependencies. An attempt was made to load a program with an incorrect format

We have just upgraded one of our projects to .Net 4.0 and have re-configured our build server (Cruise Control .Net). Anyone help with the above error? I have included more trace below.

>     debug:
>     
>          [copy] Copying 1 file to 'C:\Builds\SilverChip\Working\sc.website\web.config'.
>          [copy] Copying 1 file to 'C:\Builds\SilverChip\Working\sc.admin\web.config'.
>          [copy] Copying 1 file to 'C:\Builds\SilverChip\Working\sc.website\bin\Intelligencia.UrlRewriter.dll'.
>          [copy] Copying 1 file to 'C:\Builds\SilverChip\Working\sc.website\bin\UrlRewritingNet.UrlRewriter.dll'.
>          [exec] Microsoft (R) Build Engine Version 4.0.30319.1
>          [exec] [Microsoft .NET Framework, Version 4.0.30319.1]
>          [exec] Copyright (C) Microsoft Corporation 2007. All rights
> reserved.
>          [exec] 
>          [exec] Build started 11/05/2010 12:02:16.
>          [exec] Project "C:\Builds\SilverChip\Working\Silverchip.sln"
> on node 1 (default targets).
>          [exec] ValidateSolutionConfiguration:
>          [exec]   Building solution configuration "Debug|Any CPU".
>          [exec] Project "C:\Builds\SilverChip\Working\Silverchip.sln"
> (1) is building
> "C:\Builds\SilverChip\Working\sc.lib\sc.lib.csproj"
> (2) on node 1 (default targets).
>          [exec] CoreCompile:
>          [exec] Skipping target "CoreCompile" because all output files
> are up-to-date with respect to the
> input files.
>          [exec] _CopyAppConfigFile:
>          [exec] Skipping target "_CopyAppConfigFile" because all
> output files are up-to-date with
> respect to the input files.
>          [exec] CopyFilesToOutputDirectory:
>          [exec]   sc.lib -> C:\Builds\SilverChip\Working\sc.lib\bin\Debug\sc.lib.dll
>          [exec] Done Building Project "C:\Builds\SilverChip\Working\sc.lib\sc.lib.csproj"
> (default targets).
>          [exec] Project "C:\Builds\SilverChip\Working\Silverchip.sln"
> (1) is building
> "C:\Builds\SilverChip\Working\sc_admin.metaproj"
> (3) on node 1 (default targets).
>          [exec] Build:
>          [exec]   Copying file from "C:\Builds\SilverChip\Working\sc.lib\bin\Debug\sc.lib.dll"
> to "sc.admin\\Bin\sc.lib.dll".
>          [exec]   Copying file from "C:\Builds\SilverChip\Working\sc.lib\bin\Debug\SubSonic.Core.dll"
> to "sc.admin\\Bin\SubSonic.Core.dll".
>          [exec]   Copying file from "C:\Builds\SilverChip\Working\sc.lib\bin\Debug\sc.lib.pdb"
> to "sc.admin\\Bin\sc.lib.pdb".
>          [exec]   C:\Windows\Microsoft.NET\Framework\v4.0.30319\aspnet_compiler.exe
> -v /sc.admin -p sc.admin\ -u -f -d PrecompiledWeb\sc.admin\ 
>          [exec] ASPNETCOMPILER : error ASPCONFIG: Could not load file or
> assembly 'System.Data' or one of its
> dependencies. An attempt was made to
> load a program with an incorrect
> format.
> [C:\Builds\SilverChip\Working\sc_admin.metaproj]
>          [exec] Done Building Project "C:\Builds\SilverChip\Working\sc_admin.metaproj"
> (default targets) -- FAILED.
>          [exec] Project "C:\Builds\SilverChip\Working\Silverchip.sln"
> (1) is building
> "C:\Builds\SilverChip\Working\sc_website.metaproj"
> (4) on node 1 (default targets).
>          [exec] Build:
>          [exec]   Copying file from "C:\Builds\SilverChip\Working\sc.lib\bin\Debug\sc.lib.dll"
> to "sc.website\\Bin\sc.lib.dll".
>          [exec]   Copying file from "C:\Builds\SilverChip\Working\sc.lib\bin\Debug\SubSonic.Core.dll"
> to
> "sc.website\\Bin\SubSonic.Core.dll".
>          [exec]   Copying file from "C:\Builds\SilverChip\Working\sc.lib\bin\Debug\sc.lib.pdb"
> to "sc.website\\Bin\sc.lib.pdb".
>          [exec]   C:\Windows\Microsoft.NET\Framework\v4.0.30319\aspnet_compiler.exe
> -v /sc.website -p sc.website\ -u -f -d PrecompiledWeb\sc.website\ 
>          [exec] ASPNETCOMPILER : error ASPCONFIG: Could not load file or
> assembly 'System.Data' or one of its
> dependencies. An attempt was made to
> load a program with an incorrect
> format.
> [C:\Builds\SilverChip\Working\sc_website.metaproj]
>          [exec] Done Building Project "C:\Builds\SilverChip\Working\sc_website.metaproj"
> (default targets) -- FAILED.
>          [exec] Done Building Project "C:\Builds\SilverChip\Working\Silverchip.sln"
> (default targets) -- FAILED.
>          [exec] 
>          [exec] Build FAILED.
>          [exec] 
>          [exec] "C:\Builds\SilverChip\Working\Silverchip.sln"
> (default target) (1) ->
>          [exec] "C:\Builds\SilverChip\Working\sc_admin.metaproj"
> (default target) (3) ->
>          [exec] (Build target) -> 
>          [exec]   ASPNETCOMPILER : error ASPCONFIG: Could not load file
> or assembly 'System.Data' or one of
> its dependencies. An attempt was made
> to load a program with an incorrect
> format.
> [C:\Builds\SilverChip\Working\sc_admin.metaproj]
>          [exec] 
>          [exec] 
>          [exec] "C:\Builds\SilverChip\Working\Silverchip.sln"
> (default target) (1) ->
>          [exec] "C:\Builds\SilverChip\Working\sc_website.metaproj"
> (default target) (4) ->
>          [exec]   ASPNETCOMPILER : error ASPCONFIG: Could not load file
> or assembly 'System.Data' or one of
> its dependencies. An attempt was made
> to load a program with an incorrect
> format.
> [C:\Builds\SilverChip\Working\sc_website.metaproj]
>          [exec] 
>          [exec]     0 Warning(s)
>          [exec]     2 Error(s)
>          [exec]