I use vRoute and Skyvector both (as well as Navigraph Chart Cloud, but that is a subscription service). If it is an airway issue, for instance the FMC won't accept that airway J123 starts at waypoint 'ABCDE' or ends at waypoint 'FGHIJ' try going direct without using the airway. In your case, if that is in fact the reason for the invalid entry, just try skipping that waypoint in the plan and going to the next one in sequence. I solved that by purchasing an annual subscription to Navigraph data and then only using current real world flight plans to plan my flights. Invalid entries were usually, for me at least, entering a waypoint from a current AIRAC flightplan that did not exist in the AIRAC that came with the aircraft when I downloaded it. With the eJets FMC it is very easy to forget a step in the entry process. I found a tutorial on you tube and then paused the tutorial as I watched and wrote down the entry steps in order in to a checklist form that I still use to this day to enter my flight plans. The Position Initialization problem usually came down to me not entering a cruise altitude on the performance page. When I first used them (E170/E190) I also had trouble with Position Initialization and invalid entries. Flightplan entry is the same in both, so platform doesn't matter in this case. I also have the eJets for both FS2004 and FSX.
