Please check if there is any other error message like this:
Message: System.Web.HttpParseException: C:\Windows\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\root\69dae1a3\e3857219\App_Web__googlecheckout.ascx.37546475.mov4v8qn.0.vb(93): error BC32206: The project currently contains references to more than one version of GCheckout, a direct reference to version 1.3.0.0 and an indirect reference (through 'CATALooK.GoogleCheckOut.GCheckoutButton1') to version 1.3.3.0. Change the direct reference to use version 1.3.3.0 (or higher) of GCheckout.This means that there is an older version of the GCheckout.dll in the \bin folder of this web site. Please delete this file and re-install the module CAT_Modules.ZIP. This module includes the latest GCheckout assembly version. Often this happens if someone copies the dll manually into the \bin folder. After that the file permissions may change and the DNN installer is not longer able to overwrite the file by a newer file version that is included in a module. Or maybe you have installed another module before that includes this old GCheckout version.