This could mean that there were bubbles between gel and membrane.

Or in some cases, it could be a result of not sufficient time for gel polymerization.

Use the roller to carefully remove the bubbles trapped in between the gel and the membrane so that the transfer is complete.

Hi Luca Panarello

This is a error occurred during the transfer step, due to entrapment of air bubbles in between the transfer pads and gel. Roll over the roller properly and add sufficient amount of transfer buffer to avoid it.

Thanks,