Yes, I still get the error when trying to delete a line form the Dnn_packages table  (delete from dnn_packages where PackageID = 144)

I run select * from sys.indexes and I see those CLUSTERED index :

PK_Dnn_PackageTypes_1%
PK_Dnn_Packages *
PK_Dnn_PackageDependencies *
PK_Dnn_PackageAssemblies
PK_Dnn_LanguajePacks *
PK_Dnn_JavaScriptLibraries *
PK_Dnn_DesktopModules *
PK_Dnn_SkinControls * 
PK_Dnn_SkinPackages * 
PK_Dnn_Authentication *

First I notice that the one for the PackageTypes are "_1" and not with just the name, that shouldn't matter

And two tables that have dependencies with  Dnn_Packages are without index :

Dnn_Assemblies **
Dnn_Dashboard_Controls *

may be a missing PK on one of those tables ?

I have given a look to all the dependant tables (* are ones with PackageID fiels as Required, ** as not required) and I only found the lines 144 and 145 (the ones belonging to the skins I want to delete) on the Dnn_SkinPackages, where I delete without problem

Still, I cant delete from Dnn_Packages :: Tables without a clustered index are not supported in this version of SQL Server. Please create a clustered index and try again.