I was recently getting a fatal error warning when exiting FSX, it ran fine and only got this error on shutdown of fsx.
According to the error report it was
Fault Module Name: panels.dll
Running W7 64 FsX Gold, in the end it had nothing to do with the panel.dll or FSX but recently installed aircraft that installed microsoft visual 2015/ 2017/ 2019.
It only affected FSX and nothing else, removing the microsft visual 2015 cured the error messages and Fsx and my other games run well.
Microsoft visual 2015/2017/2019 contain the same elements.