Custom database query always the same error

Hi,
When I try to build a custom database query and try to execute it, I always get an “request failed”. And in the logs I find:

— 550 dmxConnect/api/__exec_query.php: No such file or directory

I’m not sure what that is supposed to mean. Was a temporary file creation not successful?

Single Datebase Querys using the Query Builder work and show up on my website successfully.

Thank you