CathInfo.com

Yep.  I would seek a Traditional priest and start all over with a General Confession.  Of course, the SSPX priests are instructed to tell you that the Novus Ordo Sacaraments are valid...

Though one needs to ensure that the SSPX priest was ordained by one of the SSPX bishops and not a Novus Ordo priest working with the SSPX.

How would you know it was invalid?

TKGS believes like most sedevacantists and many other trads that the Novus Ordo Holy Orders are invalid, so in his mind the man is not a valid priest so all of his absolutions are not valid.

Actually, the new rite of ordination is probably valid, though I would agree that one could have uncertainty on the issue.

It is the new rite of consecration that is invalid, so bishops consecrated in the new rite have not the power to ordain priests.

While it may be possible that the priest in question is an elderly priest or was ordained by an elderly bishop, his obvious complete ignorance of what constitutes mortal sin--or, more likely, his rejection of the very concept of mortal sin, goes to the very heart of his intentions in the confessional.

One simply cannot seriously consider the sins listed as being merely venial sins unless one has completely lost the faith and really doesn't believe the sacrament of penance has any actual value.  On the other hand, the sacraments are not valid or invalid based on the faith of the priest, so, if the priest is actually validly ordained by a real bishop, then the confession would be valid (though I wouldn't risk my salvation on it).

Ladislaus gave the best advice.