What is Sikul and Findfailed error in Sikuli ?
Sikuli is a GUI automation tool or library that uses images of the object to be automated from any given screen.
So these images are manually pre captured and stored in Sikuli automation framework if you are coding using Eclipse Java for Sikuli implementation.
After capturing the screen images, if you change windows screen resolution, Sikuli may give exceptions while execution and that error will be FindFailed exception. These exceptions will be displayed in error log or console of your IDE.