well this is going to be a hard one since you are using PLE ..because PLE files dont open up in the full program maya ...i could be wrong though ...what is that last thing you did before you could not convert ?

if you go to display >custom poly >then click on highlight borders and set the value to 5

that helps it shows you edges ..maybe you have duplicate edges in one place or take a screenie ..edges will be thicker and only suppose to have one in givin area if it is truly on an edge ...

also another thing i have found to trouble shoot ..if you go to vertices faces and see one that looks like it is on top ..then you have two faces on top and need to delete the whole face and readd it ..

if you are confused let me know ..hope that helps