lyx file from 2015 not converted to pdf

[Wolfgang Engelmann]

Am 24.03.20 um 19:29 schrieb Pavel Sanda:
> On Tue, Mar 24, 2020 at 07:21:27PM +0100, Wolfgang Engelmann wrote:
>> LyX: Software exception Detected
>> LyX has caught an exception, it will now attempt to save all unsaved
>> documents and exit.
>> Exception: std::exception
>>
>> Did I understand you correctly, that you did not receive this message?
> 
> No, but you might have assertions enabled.

what does assertion mean?

> Did you self compile or do you use distribution binary?

no, I used the Debian actualizations
Wolfgang

> 
> Pavel
>