Could you send us the save file or folder in question? It will make it much easier for us to fix it. Either give us a link here or send the file(s) directly on Discord.
Update: I copied my savegames back to the Linux machine and there it is still working. But I want to play on my big screen running windows. I watched the Malutina sequence and saved when I got free the next morning and moved the savefiles back to windows, hoping a crash won't happen again. I kept playing for a while, but when I want to confront Zhara in the town hall the game crashes again (same error) when I enter her room.
I have uploaded the new save folder. savefile 22 is right before Malutina city gate crash, savefile 24 is before entering the town hall crash:
https://www67.zippyshare.com/v/n6voMDr6/file.html
Would be great if you could do anything to help. I could continue playing on Linux but I want to enjoy the game on the big screen. I don't want to start from scratch on windows (because I can't even be sure if the Linux-widows-switch really is the cause of the problem, I only read in an rpgmaker forum that the "header is wrong" error could be caused by an incompatible savefile, so I assume starting on Linux and moving to windows is the cause of the problem).
One more thing I noticed (don't know if it's important): There seems to be something wrong with Arden. She never changes her appearance and always looks like she is wearing her standard outfit. I think it's been that way since the mission when you get the maid outfit. After she changed back into her normal clothes (storywise) I could never get her to wear the maid costume again (regarding to appearance) when I equip it. Equipping casual clothes doesn't change her looks either. I just hope my savegame isn't entirely effed up.
After defeating Casca you got the Gem of Illusion key item. That item lets you force the game to always show a party member in one outfit, no matter what they actually wear. Try using that item again, toggling off your selection for Aden.
As for the Linux issue, I'm still looking into that. It's a little difficult without owning a Linux myself 😅
Oh, dammit! I am sooooo sorry for the trouble I have caused you, just tie me up and put me in a cave. When I googled the error message and read it COULD BE caused by incompatible savefiles due to platform switching I assumed that was the case here. So I forgot thinking about other possible causes, including the most obvious one. Now I did some further testing and it turned out it was caused by a broken game install or damaged game files on the windows machine. When I downloaded the game again and reinstalled it, everything seems to be working. Stop looking into the issue, there is nothing wrong with the game or my savefiles, the error was on my computer's side and must have been caused by a bad file transfer when I moved the gamefiles via USB-Drive to the Windows machine (because it doesn't have an internet connection, it's a retro games emulation console running windows under the hood). Again, I'm so sorry for troubling you with this. After the reinstall everything seems to be working.
Na, it's not entirely on you, normally I am tech-savvy enough that I should have thought about re-installing earlier myself. Thanks for the info with the Gem of Illusions, I remember getting it and trying it out once, but I misunderstood its purpose and thought it was for previewing or browsing through costumes without having to equip them. As I didn't have many costumes at this point (just the maid) I didn't use it again and then forgot about having that item later.