Let's back up a step or two.  Based on your wording, it sounds like you are trying to convert and transmit in one step.  So I'm not sure if it is a conversion issue or a transmission issue.  Try doing it in two steps.  Try converting the file for e-filing.  If that works, then go to the second step and try transmitting the return.  That way we can see where there hiccup is.  Before you do that though, try rebooting your computer.