I posted this on the dnncreative.com forum and they suggested I try here:

Recently upgraded to 5.01.00. All modules seem to be working but when I go to the Module Definitions area in the host menu, this is what I get:

Error: Module Definitions is currently unavailable.
DotNetNuke.Services.Exceptions.ModuleLoadException: C:\Inetpub\wwwroot\DotNetNuke\Admin\ModuleDefinitions\ModuleDefinitions.ascx.vb(61): error BC30311: Value of type 'String' cannot be converted to 'System.Version'. ---> System.Web.HttpCompileException: C:\Inetpub\wwwroot\DotNetNuke\Admin\ModuleDefinitions\ModuleDefinitions.ascx.vb(61): error BC30311: Value of type 'String' cannot be converted to 'System.Version'. 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.UI.ControlUtilities.LoadControl[T](TemplateControl containerControl, String ControlSrc) at DotNetNuke.UI.Modules.ModuleHost.LoadModuleControl() --- End of inner exception stack trace ---

Can anyone suggest a solution? I have yet to run across anything that resolves it.

I just upgraded to 5.1.1 and I'm still getting this error.

Module Definitions is still visible in the host menu. Plus Extensions, is not visible.

When upgrading I did get an error: 00:00:00.062 - Executing Script: 05.01.01.SqlDataProvider Error! (See 05.01.01.log for more information).

Here's the log:

System.Data.SqlClient.SqlException: 'DF_Packages_IsSystemPackage' is not a constraint.
Could not drop constraint. See previous errors.
   at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection)
   at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection)
   at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj)
   at System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj)
   at System.Data.SqlClient.SqlCommand.RunExecuteNonQueryTds(String methodName, Boolean async)
   at System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(DbAsyncResult result, String methodName, Boolean sendToPipe)
   at System.Data.SqlClient.SqlCommand.ExecuteNonQuery()
   at DotNetNuke.Data.SqlDataProvider.ExecuteADOScript(String SQL)
   at DotNetNuke.Data.SqlDataProvider.ExecuteScript(String Script, Boolean UseTransactions)

/* Fix bug in drop index in 5.0 script - replay failed part of script */
/**********************************************************************/

ALTER TABLE nuke1.Packages DROP CONSTRAINT DF_Packages_IsSystemPackage

CREATE TABLE nuke1.Tmp_Packages
 (
 PackageID int NOT NULL IDENTITY (1, 1),
 PortalID int NULL,
 Name nvarchar(128) NOT NULL,
 FriendlyName nvarchar(250) NOT NULL,
 [Description] nvarchar(2000) NULL,
 PackageType nvarchar(100) NOT NULL,
 [Version] nvarchar(50) NOT NULL,
 License ntext NULL,
 Manifest ntext NULL,
 [Owner] nvarchar(100) NULL,
 Organization nvarchar(100) NULL,
 Url nvarchar(250) NULL,
 Email nvarchar(100) NULL,
 ReleaseNotes ntext NULL,
 IsSystemPackage bit NOT NULL,
 CreatedByUserID int NULL,
 CreatedOnDate datetime NULL,
 LastModifiedByUserID int NULL,
 LastModifiedOnDate datetime NULL
 )
 
ALTER TABLE nuke1.Tmp_Packages ADD CONSTRAINT DF_Packages_IsSystemPackage DEFAULT ((0)) FOR IsSystemPackage

SET IDENTITY_INSERT nuke1.Tmp_Packages ON

IF EXISTS(SELECT * FROM nuke1.Packages)
  EXEC('INSERT INTO nuke1.Tmp_Packages (PackageID, PortalID, Name, FriendlyName, Description, PackageType, Version, License, Manifest, Owner, Organization, Url, Email, ReleaseNotes, IsSystemPackage, CreatedByUserID, CreatedOnDate, LastModifiedByUserID, LastModifiedOnDate)
  SELECT PackageID, PortalID, Name, FriendlyName, Description, PackageType, Version, License, Manifest, Owner, Organization, Url, Email, ReleaseNotes, IsSystemPackage, CreatedByUserID, CreatedOnDate, LastModifiedByUserID, LastModifiedOnDate FROM nuke1.Packages WITH (HOLDLOCK TABLOCKX)')

SET IDENTITY_INSERT nuke1.Tmp_Packages OFF

ALTER TABLE nuke1.Assemblies DROP CONSTRAINT FK_PackageAssemblies_PackageAssemblies

ALTER TABLE nuke1.DesktopModules DROP CONSTRAINT FK_DesktopModules_Packages

ALTER TABLE nuke1.LanguagePacks DROP CONSTRAINT FK_LanguagePacks_Packages

DROP TABLE nuke1.Packages

EXECUTE sp_rename N'nuke1.Tmp_Packages', N'Packages', 'OBJECT'

ALTER TABLE nuke1.Packages ADD CONSTRAINT PK_Packages PRIMARY KEY CLUSTERED ( PackageID )

CREATE UNIQUE NONCLUSTERED INDEX IX_Packages ON nuke1.Packages ( Owner, Name, PortalID )

ALTER TABLE nuke1.LanguagePacks ADD CONSTRAINT FK_LanguagePacks_Packages FOREIGN KEY ( PackageID ) REFERENCES nuke1.Packages ( PackageID ) ON UPDATE  NO ACTION ON DELETE  CASCADE
 
ALTER TABLE nuke1.DesktopModules WITH NOCHECK ADD CONSTRAINT FK_DesktopModules_Packages FOREIGN KEY ( PackageID ) REFERENCES nuke1.Packages ( PackageID ) ON UPDATE  CASCADE ON DELETE  CASCADE

ALTER TABLE nuke1.Assemblies ADD CONSTRAINT FK_PackageAssemblies_PackageAssemblies FOREIGN KEY ( PackageID ) REFERENCES nuke1.Packages ( PackageID ) ON UPDATE  NO ACTION ON DELETE  CASCADE
 

How can I fix this?
 

 Good news - restored to 5.00.01 - and retried upgrade and everything was a success!  PHEW!  The site is a large one and I'd have hated to try and move it!