new calipers wierd problem?

[irondiezl3]

put some new calipers on today everything went great until the very end one side after bleeding just fine all the sudden wouldnt bleed at all. meaning it stopped pumping fluid whatsoever out. we checked everything over and over fluid was full pedal was fine no leaks anywhere just all the sudden nothing would come out. if i pulled the bleeder screw completely out then the fluid would come out. once i put the bleeder screw in even lose it wouldnt bleed. i checked with a bright loght there are no clogs anywhere. i tried a new bleeder screw same issue. i apologize for the spelling and grammer im just so frustrated does anyone have any idea what could be going on??