dropped stitch at end of row?

[SallyG]

Hi all! Can anyone help? I'm knitting a Cardigan in stocking stitch and a loop has suddenly appeared at the end of a row suggesting I've dropped a stitch, but I've still got the correct number of stitches. Have I managed to miss a couple of rows while holding on to the one stitch? I've unpicked a coule of rows but probably just moved the problem down lol! Help! Slightly confused.