Oki doki...

i will try to see if I can explain what I mean...

1. some of the techniqes I use you can see here...

2. I don't know if you have the PolyCount on... (Display... --> heads up disply... --> Poly count...) but if you have you can see how many vertices there are... if you then select the vertice, you can see if it is 1 or 2 vertices... (purple colour on attached image)

3. you can also try show faces... and then try to see if there is a "Blue Dot" along the edge you want to delete... if there is a blue dot, try to delete it, before deleting the edge... (orange colour on attached image)...

it might also be that they the two edges aren't merged together properly... e.g. that the one edge need to be splitted... see yellow colour on attached image...

btw. what value did you use with the merge?

regards

Strarup