UPDATE README.md

Author: PhMueller

README.md

@@ -139,6 +139,10 @@ If you use a benchmark in your experiments, please specify the version number of
 the used container to ensure reproducibility. When starting an experiment, HPOBench writes automatically these two version numbers to the log. 
 
 ### Troubleshooting and Further Notes
+  - **Singularity throws an 'Invalid Image format' exception**
+  Use a singularity version >= 3.8. If you have multiple singularity installations, you have to add the correct singularity version to your $PATH, e.g.
+  ```export PATH=/usr/local/kislurm/singularity-3.8/bin/:$PATH```
+
   - **A Benchmark fails with `SystemError: Could not start an instance of the benchmark. Retried 5 times` but the container 
 can be started locally with `singularity instance start <pathtocontainer> test`**
 See whether in `~/.singularity/instances/sing/$HOSTNAME/*/` there is a file that does not end with '}'. If yes delete this file and retry.