I have same troubles with nebula coaddition

I have same troubles with nebula coaddition.
Look at the attached screenshot

Info about used data:
instrument - VLT@OmegaCam
object name - Messier 42
filter - R_SDSS
number of frames - 3
Look at the attached screenshot

Info about used data:
instrument - VLT@OmegaCam
object name - Messier 42
filter - R_SDSS
number of frames - 3