I know this post is OLD. Just answering anyway, in case anybody else has problems with this.
I got the same error message when testing minimus2 recently, and it turns out this was NOT because no overlaps would be detected (would have hoped for a more informative message on that, anyway).
Turns out, the standard error-output of minimus2 is not very helpful. You have to check the ".runAmos.log" file for actual info on what went wrong. (in your case that would be "all_velvet.runAmos.log".
In my case I found that minimus was expecting the tools delta-filter and show-coords at /usr/local/bin. However this may not be the case if you installed amos locally on a shared server, where you have no admin rights (as I did via bioconda).
Therefore you may have to manually edit the minimus2 script at lines 46 & 47 to point to the correct executables.
Solved the problem for me!