Hi guys, some updates to your question.
did you take the capitalshipinfo back to 5? it seems the game will not allow more than that for cap ship types.
Yeah, I did, unfortunately no luck for me

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To the original poster: I haven't tried this myself yet, but did you also copy and rename a mesh file for the ship to match the name of the new entity file? You may also need to copy and rename texture files. Not having any defined graphics/model for the ship could be causing your dump.
Actually the reason for my multiple dumps was I use my new strings from english.str, I can use and modify current strings without any issues, but not newly inputed one. I figured out that order capitalships strings MUST be in the same order as in
PlayerTech.entity, once I moved my BATTLECRUISER ID and DESCRIPTION from the bottom of the file to the rest of the IDS_CAPITALSHIP_TECH* strings, it works and no more dumping!
Update: I removed one of the existing capital entries in english.str and now my new capital shows up in the last spot, buildable and everything, no crashes. So it is obviously a UI problem.
Which is a bit daft... not having the buttons automatically spill over to the second row. I'll check out frigates, maybe the answer is there.
Yeah, I trying to figure out this issue with no luck this morning. I got around this issue by putting my new ship in the 5th slot. I guess I got to work now

, at least my new battlecruiser works like a beaut now!