Could you give the following report a try:
Select Top 1000000 tblAssets.AssetID,
  tblAssets.AssetName,
  tUptime.[Last power on time],
  tsysAssetTypes.AssetTypeIcon10 As icon,
  tblAssets.Lastseen As [Last scan],
  Ceiling(tblAssets.Uptime /
  3600) As [uptime since boot up during last scan (h)],
  tblAssets.Username As [Last user logged on]
From tblAssets
  Inner Join tblAssetCustom On tblAssets.AssetID = tblAssetCustom.AssetID
  Inner Join tsysAssetTypes On tsysAssetTypes.AssetType = tblAssets.Assettype
  Left Join (Select tblUptime.AssetId,
    Max(tblUptime.EventTime) As [Last power on time]
  From tblUptime
  Where tblUptime.EventType In (1, 4)
  Group By tblUptime.AssetId) tUptime On tUptime.AssetId = tblAssets.AssetID
Where tblAssetCustom.State = 1 And tblAssets.Assettype = -1
Order By tblAssets.AssetName