Hi community,

after a very long time of investigating I found the reason: missing indexes!

I know, above I wrote that I checked & created them, but somehow this didn't work correctly and I only found out after hours and hours of testing :-/ However, it looks as if the upgrade drops several veeeeeery important indexes on the database, which makes the media nodes nearly unuseable! I made a database diff between a new created database of Umbraco and my upgarded database and found several differences - some of them are indexes - and obviously some are essential for the media nodes to work!

@Umbraco team: please look into this - especially what else might be missing in upgraded databases :-)

@all others: the solution that worked for me:

1) Use the SQL CE Toolbox (http://sqlcetoolbox.codeplex.com/) if you are using SQL CE or a SQL Editor and open a connection to your Umbraco database (of course backup before :-)

2) Execute the statements below on your database (it could be that some indexes are missing, are too much or not necessary, but these are the ones that were identified as missing between a new installation & my database. There are also some other stataments in the difference analysis (like constraints and defaults) but I left them out as all other things seem to work quite well...):

CREATE UNIQUE INDEX [IX_cmsContent] ON [cmsContent] ([nodeId] ASC);
GO
CREATE UNIQUE INDEX [IX_cmsContentType] ON [cmsContentType] ([nodeId] ASC);
GO
CREATE INDEX [IX_cmsContentType_icon] ON [cmsContentType] ([icon] ASC);
GO
CREATE UNIQUE INDEX [IX_cmsContentVersion_VersionId] ON [cmsContentVersion] ([VersionId] ASC);
GO
CREATE UNIQUE INDEX [IX_cmsDataType_nodeId] ON [cmsDataType] ([nodeId] ASC);
GO
CREATE UNIQUE INDEX [IX_cmsDictionary_id] ON [cmsDictionary] ([id] ASC);
GO
CREATE UNIQUE INDEX [IX_cmsDocument] ON [cmsDocument] ([nodeId] ASC,[versionId] ASC);
GO
CREATE UNIQUE INDEX [IX_cmsDocument] ON [cmsDocument] ([nodeId] ASC,[versionId] ASC);
GO
CREATE INDEX [IX_cmsPropertyData_1] ON [cmsPropertyData] ([contentNodeId] ASC);
GO
CREATE INDEX [IX_cmsPropertyData_2] ON [cmsPropertyData] ([versionId] ASC);
GO
CREATE INDEX [IX_cmsPropertyData_3] ON [cmsPropertyData] ([propertytypeid] ASC);
GO
CREATE INDEX [IX_cmsTaskType_alias] ON [cmsTaskType] ([alias] ASC);
GO
CREATE UNIQUE INDEX [IX_cmsTemplate_nodeId] ON [cmsTemplate] ([nodeId] ASC);
GO
CREATE UNIQUE INDEX [IX_umbracoLanguage_languageISOCode] ON [umbracoLanguage] ([languageISOCode] ASC);
GO
CREATE INDEX [IX_umbracoLog] ON [umbracoLog] ([NodeId] ASC);
GO
CREATE INDEX [IX_umbracoNodeObjectType] ON [umbracoNode] ([nodeObjectType] ASC);
GO
CREATE INDEX [IX_umbracoNodeParentId] ON [umbracoNode] ([parentID] ASC);
GO

After that the media nodes worked like a charm :-)

I hope that helps...