Passed urine test, then failed, no smoking??

I have to take urine tests for probation. I was a pot smoker, but have not smoked for quite some time. I passed my first two tests, and then out of nowhere failed my second two. I have not smoked since I started taking the tests, so I am very confused about how this could have happened. Anyone have any ideas???

I wanted to add this so there is no confusion..I stopped smoking a little more than a month ago, I am a 5'1.5" 101.5 lb female.

That all depends on how long you consider "quite some time" . To be honest maybe 1 in a 1000 over the counter tests "maybe" it will give a false positive if you are completely clean, but I doubt it. So the fact that you failed on 2 is kinda telling me "A" your still smoking.......Or "B" you stopped smoking less than a month ago or about a month ago is you are overweight. Something tell's me that you are not telling us everything. If you have more info put it out there or you wont get an accurate answer. Also if you want to know more them hit up my profile and email me since I wont be able to respond again after this post.

perhaps your sample could have been contaminated. maybe by hygenic products?

wow dude, i feel your pain. the only reasonable answer i have to this. other than fattie tissue dissolving that was holding onto some thc... is one of your hairs diluting the test sample. i dont know if that is even possible. but thats the only thing i got. four2oh is right around the corner. wish i could join you. :] plur.

If you have worked out recently it can show THC in your system, because it is stored in the fat cells of your body.