I've solved the above problem by altering the manifest: type had to be "Package" instead of "Module". So now I've successfully installed the Authentication, but now when I go to the login page I receive the following error: 

A critical error has occured.
Could not load type 'DotNetNuke.Authentication.Intranet.Login'.

The dll file has been installed in the Bin/Providers folder, but I still keep getting this error.
This is the detailed error from the logfiles:

AssemblyVersion: 04.08.02
PortalID: 0
PortalName: Intranet
UserID: -1
UserName:
ActiveTabID: 41
ActiveTabName: Login
RawURL: /login.aspx
AbsoluteURL: /Default.aspx
AbsoluteURLReferrer:
UserAgent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729; InfoPath.2)
DefaultDataProvider: DotNetNuke.Data.OracleDataProvider, DotNetNuke.OracleDataProvider
ExceptionGUID: 2417f3c2-0407-49a3-9da8-a22ccb844a77
InnerException: Could not load type 'DotNetNuke.Authentication.Intranet.Login'.
FileName:
FileLineNumber: 0
FileColumnNumber: 0
Method: System.Web.UI.TemplateParser.GetType
StackTrace:
Message: DotNetNuke.Services.Exceptions.PageLoadException: Could not load type 'DotNetNuke.Authentication.Intranet.Login'. ---> System.Web.HttpParseException: Could not load type 'DotNetNuke.Authentication.Intranet.Login'. ---> System.Web.HttpParseException: Could not load type 'DotNetNuke.Authentication.Intranet.Login'. ---> System.Web.HttpException: Could not load type 'DotNetNuke.Authentication.Intranet.Login'. at System.Web.UI.TemplateParser.GetType(String typeName, Boolean ignoreCase, Boolean throwOnError) at System.Web.UI.TemplateParser.ProcessInheritsAttribute(String baseTypeName, String codeFileBaseTypeName, String src, Assembly assembly) at System.Web.UI.TemplateParser.PostProcessMainDirectiveAttributes(IDictionary parseData) --- End of inner exception stack trace --- at System.Web.UI.TemplateParser.ProcessException(Exception ex) at System.Web.UI.TemplateParser.ParseStringInternal(String text, Encoding fileEncoding) at System.Web.UI.TemplateParser.ParseString(String text, VirtualPath virtualPath, Encoding fileEncoding) --- End of inner exception stack trace --- at System.Web.UI.TemplateParser.ParseString(String text, VirtualPath virtualPath, Encoding fileEncoding) at System.Web.UI.TemplateParser.ParseReader(StreamReader reader, VirtualPath virtualPath) at System.Web.UI.TemplateParser.ParseFile(String physicalPath, VirtualPath virtualPath) at System.Web.UI.TemplateParser.ParseInternal() at System.Web.UI.TemplateParser.Parse() at System.Web.UI.TemplateParser.Parse(ICollection referencedAssemblies, VirtualPath virtualPath) at System.Web.Compilation.BaseTemplateBuildProvider.get_CodeCompilerType() at System.Web.Compilation.BuildProvider.GetCompilerTypeFromBuildProvider(BuildProvider buildProvider) at System.Web.Compilation.BuildProvidersCompiler.ProcessBuildProviders() at System.Web.Compilation.BuildProvidersCompiler.PerformBuild() at System.Web.Compilation.BuildManager.CompileWebFile(VirtualPath virtualPath) at System.Web.Compilation.BuildManager.GetVPathBuildResultInternal(VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile) at System.Web.Compilation.BuildManager.GetVPathBuildResultWithNoAssert(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile) at System.Web.Compilation.BuildManager.GetVPathBuildResult(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile) at System.Web.UI.TemplateControl.LoadControl(VirtualPath virtualPath) at System.Web.UI.TemplateControl.LoadControl(String virtualPath) at DotNetNuke.Modules.Admin.Authentication.Login.BindLogin() in C:\Inetpub\vhosts\intranet1.bdb.be\Admin\Authentication\Login.ascx.vb:line 310 at DotNetNuke.Modules.Admin.Authentication.Login.ShowPanel() in C:\Inetpub\vhosts\intranet1.bdb.be\Admin\Authentication\Login.ascx.vb:line 443 at DotNetNuke.Modules.Admin.Authentication.Login.Page_Load(Object sender, EventArgs e) in C:\Inetpub\vhosts\intranet1.bdb.be\Admin\Authentication\Login.ascx.vb:line 637 at System.Web.UI.Control.OnLoad(EventArgs e) at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) --- End of inner exception stack trace ---
Source:
Server Naam: SRVDMZ12

It sounds like when it was installed it didn't get added to all the necessary tables. I don't have a database in front of me but check the AuthenticationTypes (?) table and see if there's a entry for your provider.