Im trying to upgrade a umbraco 4.0.2 implementation to 4.7.2.

I've done a by-the-book upgrade, which seemed to be working just fine...
Until i've started extending it.

I made a template out of mistake and deleted it. Afterwards the Templates node structure couldnt be extended.
When i try to expand it, this 500 is throwned from http://whatever.local/umbraco/webservices/TreeDataService.ashx?rnd=491dace566cd472d8228e38a1e7661e5&id=-1&treeType=templates&contextMenu=true&isDialog=false&rnd2=2.5:
[NullReferenceException: Object reference not set to an instance of an object.]
   umbraco.cms.businesslogic.template.Template.getMasterPageContent() +73
   umbraco.cms.businesslogic.template.Template.setupNode() +397
   umbraco.cms.businesslogic.template.Template.GetAllAsList() +298
   umbraco.loadTemplates.RenderTemplates(XmlTree& tree) +85
   umbraco.presentation.webservices.TreeDataService.GetXmlTree() +135
   umbraco.presentation.webservices.TreeDataService.ProcessRequest(HttpContext context) +85
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +595
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +265

It turns out that when i delete templates, document- and data types the call throws a 500-error like:
"Message":"Umbraco Exception (DataLayer): SQL helper exception in ExecuteNonQuery","StackTrace":" at umbraco.DataLayer.SqlHelper`1.ExecuteNonQuery(String commandText, IParameter[] parameters)\r\n at umbraco.cms.businesslogic.Tags.Tag.RemoveTagsFromNode(Int32 nodeId)\r\n at umbraco.cms.businesslogic.CMSNode.delete()\r\n at umbraco.cms.businesslogic.template.Template.delete()\r\n at umbraco.templateTasks.Delete()\r\n at umbraco.presentation.webservices.legacyAjaxCalls.Delete(String nodeId, String alias, String nodeType)","ExceptionType":"umbraco.DataLayer.SqlHelperException"

The consquence of the error is that the lines in umbracoNode is left untouched.

Contents nodes seems to be deleted correctly, but when deleting em from the Recycle bin, i get a 500 telling me:
"Message":"Umbraco Exception (DataLayer): SQL helper exception in ExecuteNonQuery","StackTrace":" at umbraco.DataLayer.SqlHelper`1.ExecuteNonQuery(String commandText, IParameter[] parameters)\r\n at umbraco.cms.businesslogic.Tags.Tag.RemoveTagsFromNode(Int32 nodeId)\r\n at umbraco.cms.businesslogic.CMSNode.delete()\r\n at umbraco.cms.businesslogic.Content.delete()\r\n at umbraco.cms.businesslogic.web.Document.DeletePermanently()\r\n at umbraco.presentation.webservices.legacyAjaxCalls.DeleteContentPermanently(String nodeId, String nodeType)","ExceptionType":"umbraco.DataLayer.SqlHelperException"

I've tried everything i can find. I've tried to upgrade to 4.5.2, that http://www.proworks.com/blog/2011/03/03/my-notes-and-experiences-upgrading-umbraco-4-0-x-to-4-6-1/ suggests, followed the guides in the official Umbraco wiki, and i've tried this guide: http://blue-and-orange.net/articles/umbraco/upgrading-umbraco-to-47/

Also, i've tried changing the DELETE statements suggested in http://anthonydotnet.blogspot.com/2010/12/cannot-delete-document-type-umbraco.html (on the tables involved and the rolled back when the turned out not to work).

No luck.

My guess is that the SP's rather than the structure of the DB is wrong, i havn't checked it though - i don't really want to mess with the DB.

Does anyone had this problem?
How do i solve it?