For more complicated reports, I use SSMS query analyzer on the server, make my queries, and from there, insert it in to the database - as the report writer/GUI does not work with some SQL syntax/functions.
Here's what they told me for my support ticket
•	Make a backup of your database
•	Run the first query below and insert a Reportquery name and Reporttitle:
Insert Into tsysreports ( [Reportquery],[Reporttitle]) Values('MyReportQueryName', 'MyReportTitle')
•	Once the first query has been run we can run a second query to insert your report query to the database. Replace the green highlighted query with your query do note that you may have to replace any single quotes in the report query with double quotes to avoid any issues to insert it. Finally replace the yellow highlighted code with the Reportquery name that you gave in previously:
Insert Into tsysDBobjects(Query, DBobjName) Values('Select distinct assetid,backedupto = STUFF((Select distinct tblassets.assetid,'', '' + tblAssets4.assetname as backedupto 
                     from tblAssets 
                     left Join (Select distinct tsysAssetRElationTypes.Name, tsysAssetRelationTypes.RelationTypeID,tblassets.assetname, tblAssetRelations.ParentAssetID,tblAssetRelations.ChildAssetID from tblAssets 
                           Left Join tblAssetRelations On tblAssetRelations.ChildAssetID = tblAssets.AssetID 
                           Left Join tsysAssetRelationTypes On tsysAssetRelationTypes.RelationTypeID = tblAssetRelations.Type 
                           Where tsysAssetRelationTypes.Name = ''backed up to'') As RR 
                     On RR.ChildAssetId = tblassets.assetid 
                     Left Join tblAssetRelations On tblAssetRelations.ChildAssetID = tblAssets.AssetID 
                     Left Join tsysAssetRelationTypes On tsysAssetRelationTypes.RelationTypeID = tblAssetRelations.Type 
                     Left Join tblAssets tblAssets4 On tblAssets4.AssetID = rr.ParentAssetID 
              Where tsysAssetRelationTypes.Name = ''backed up to'' and tblassets.assetid=ttt.assetid 
              group by '', '' + tblassets4.assetname, tblassets.assetid 
       FOR XML PATH(''''), TYPE).value(''.[1]'', ''nvarchar(max)''), 1, 4, '''') 
       from 
              tblassets as TTT 
       Group by assetid', 'MyReportQueryName')
•	The report can now be found in the Lansweeper Reports section and be run.