Now I uninstalled the texlive version of ConTeXt and did a total new 
install of the standalone version. That did not help at all. There's 
something wrong happening within the mtxrun.

I added a new "compiler" to TeXworks that only executes the command 
printenv and it lists the following environment settings:

TEXROOT=/usr/local/context/tex

PATH=/usr/local/context/texmf-linux-64:/usr/local/context/bin:/usr/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/usr/local/context/texmf-linux-64/bin 


OSFONTDIR=/usr/local/share/fonts;/usr/share/fonts;/home/thomas/.local/share/fonts 


They look pretty correct to me. But still mtxrun complains:

----------------------------------------------

... resolvers | resolving | warning: no lua configuration files found

resolvers | resolving | no texmf paths are defined (using TEXMF)

resolvers | resolving |

mtxrun | the resolver databases are not present or outdated

...

resolvers | resolving | warning: no lua configuration files found

resolvers | resolving | no texmf paths are defined (using TEXMF)

...

mtxrun | unknown script 'context.lua' or 'mtx-context.lua'

----------------------------------------------

Clueless greetings -- Thomas

Am 09.05.2016 um 13:02 schrieb Thomas Fehige:
> To prevent misunderstandings: This is /not/ the solution, the problem 
> remains that the newly installed standalone mtxrun doesn't find 
> certain configuration files and complains about an outdated something 
> or other, /when started from within TeXworks/, while everything works 
> fine from the command line.
>
> Am 07.05.2016 um 12:49 schrieb Thomas Fehige:
>> Am 06.05.2016 um 10:04 schrieb Mojca Miklavec:
>>> Can you check the paths in the fourth tab (= Typesetting) of 
>>> Preferences/Settings? It is possible that you have more than one 
>>> version of ConTeXt installed and that you see different paths in the 
>>> Terminal than in the GUI. Mojca
>>
>> Yes I have two versions of ConTeXt. I have TeXlive from the Ubuntu 
>> repository and now the newer version as standalone. I added the paths 
>> to the new version at the top of that list in TeXwoks' preferences. 
>> And it does find and run the new version of mtxrun.
>>
>> Cheers -- Thomas
>> ___________________________________________________________________________________ 
>>
>> If your question is of interest to others as well, please add an 
>> entry to the Wiki!
>>
>> maillist : ntg-context@ntg.nl / 
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>> archive  : http://foundry.supelec.fr/projects/contextrev/
>> wiki     : http://contextgarden.net
>> ___________________________________________________________________________________
>
>
>
> ___________________________________________________________________________________
> If your question is of interest to others as well, please add an entry to the Wiki!
>
> maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
> webpage  : http://www.pragma-ade.nl / http://tex.aanhet.net
> archive  : http://foundry.supelec.fr/projects/contextrev/
> wiki     : http://contextgarden.net
> ___________________________________________________________________________________