UMG blueprint unresolved compile error when i run my game

Hello, i’ve upgraded today to 4.8 and every time i run the editor with my project i get unresolved compile error on some UMG widgets i use to draw the slots of my inventory. If i go to the slot parent class, it has the green checkbox on the compile button, so it has been compiled. If i press it again and run the game he no longer gives me error on the child widgets. If i restart the editor, the problem happens again. On the output window of Visual Studio i get this error for the 4 umg widgets:

[2015.06.11-15.20.00:398][  0]LogBlueprint:Error: [compiler GearSlot] Error This blueprint (self) is not a TRASHCLASS_BaseSlot_253, therefore ' Target ' must have a connection.
[2015.06.11-15.20.00:408][  0]LogBlueprint:Warning: [compiler GearSlot] Warning [0015.57] Compile of GearSlot failed. 1 Fatal Issue(s) 0 Warning(s) [in 21 ms]
[2015.06.11-15.20.00:409][  0]LogBlueprint:Warning: [compiler GearSlot] Warning [0015.57] Compile of GearSlot failed. 1 Fatal Issue(s) 1 Warning(s) [in 0 ms]