Got this error when I tried to load a cover art picture from the path

  /home/mast/music/various/Mitek: Process/cover.jpg

using the "Choose New Cover Art..." action:

[Warn  03:43:19.698] Caught an exception - System.UriFormatException: URI scheme must start with a letter and must consist of one of alphabet, digits, '+', '-' or '.' character. (in `System')
  at System.Uri.Parse (UriKind kind, System.String uriString) [0x00000] in <filename unknown>:0 
  at System.Uri.ParseUri (UriKind kind) [0x00000] in <filename unknown>:0 
  at System.Uri..ctor (System.String uriString, Boolean dontEscape) [0x00000] in <filename unknown>:0 
  at System.Uri..ctor (System.String uriString) [0x00000] in <filename unknown>:0 
  at Banshee.Collection.Gui.CoverArtEditor+EditorBox.SetCoverArt (Banshee.Collection.TrackInfo track, System.String path) [0x00000] in <filename unknown>:0 
  at Banshee.Collection.Gui.CoverArtEditor+EditorBox.<EditorBox>m__15 (System.Object , System.EventArgs ) [0x00000] in <filename unknown>:0 

I managed to use the picture by first copying it to another dir without ":". I also got a very similar error for another directory containing ":", while other directories worked fine, hence my conclusion that ":" is the problem.