Can't load or launch my vessel, after removing a part. Error message.

[DennisB]

I'm working on a  rocket for a challenge. I've reached my part limit, and my rocket suddenly exploded after the launch. Then I tried to redesign it to lower the number of parts, but after I remove a specific fuel tank, a problem occurs. As long as I'm working in the VAB, everything looks fine, but if I want to launch the rocket or press Ctrl+Z or try to load it, I get an error message "Part 4293965038 missing" and my rocket is gone.

Is there a way to fix it, and remove that fuel tank without the error message? Because I spent several evenings working on this project, and I want to keep the main parts of my vessel.

I have version 1.12 with DLCs without mods running on Windows 10.

[DennisB]

Problem solved.

After I deleted the problem part, I saved the three sides of the vessel as sub-assemblies, and they were not broken. I took the central part from an older save and attached the side elements to it.