It is not unusual to have some episodes of vaginal spotting when using the progestogen(Crinone) inserts. They can dry the vaginal skin and cause superficial abrasions which bleed when the pessary is inserted.
In addition, some centres also use low-dose aspirin as a supplementary drug to enhance blood flow to the endometrium. These have the effect of thinning the blood and cause minor bleeds which seem to be worse then they actually are.
The vaginal bleeds are not necessarily a sign of failed implantation. The true test of a successful implantation would be a positive pregnancy test as early as 10 days after the Embryo transfer.