Output log file from command line doesn't work

Our customer uses Keil MDK 5.12 with an LPC1768 Compiler and our application communicates via the UVSOCK Interface.

To find the source of an error which appears only in a certain environment in conjunction with jenkins, i need to get the logs.

Unfortunately as in the very old post with similar title, the -o Option of keil uVision doesnt produce an output file.

The call is C:\Keil\UV4\UV4.exe Sim_LPC1768.uvprojx -j0 -o "t:\72367\source\_build\unittests\ARM\.log\keil_v5_uv4.log" and the directory exists before uv4 is called.

Please advise how to proceed.

BTW: The error is error number 9 UV_STATUS_NOT_FOUND           = 9,  ///< Operation failed: File / group not found in the current project

Thanks for help