Been getting this the last few server restarts, and don't have the feintest idea what it means.

Exception while calling NextTick callback (NullReferenceException: Object refere
nce not set to an instance of an object)
  at Oxide.Plugins.ImageLibrary.AddImage (System.String url, System.String image
Name, System.UInt64 imageId, System.Action callback) [0x00049] in <03fc0c1750b84
566a5faa11ab528fbcf>:0
  at Oxide.Plugins.SimpleLogo.AddImage (System.String shortname) [0x00093] in <0
3fc0c1750b84566a5faa11ab528fbcf>:0
  at Oxide.Plugins.SimpleLogo+<AddImage>c__AnonStorey0.<>m__0 () [0x00000] in <0
3fc0c1750b84566a5faa11ab528fbcf>:0
  at Oxide.Core.OxideMod.OnFrame (System.Single delta) [0x00051] in <4452f821def
6406d834e4149849fe7ea>:0​

Can anyone tell me how to fix it please?

Hey,
I just push an update today, let me know if it fix it please

Yep, that seems to have fixed it mate, cheers.