Hi,
You could select Export Packet Dissections->As Plain Text (or other format you want)
If you select As Plain Text, the document will be saved as below:
As for the error, it suggests please report this to the developers of the program. Since Wireshark is a third party product, I would suggest you could contact Wireshark support for further help.
https://ask.wireshark.org/questions/
Best Regards,
Sunny
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