The error in the logs seem to be saying that the bundle command cannot be found. Meaning the bundler gem is not installed or something.
It should be related to this question in SO. You can follow the link within to the OpenShift Bug Report.
The problem is that with the previous OpenShift update, the Ruby 1.9 cartridge is supposed to be using Ruby 1.9.3 but it somehow got changed to Ruby 1.8 instead. Thus, many of the gems installed with Ruby 1.9 will not be found when it is using Ruby 1.8. The workaround is to export the PATH and LD_LIBRARY_PATH in the cron script (refer to the bug report).
Noticed you tried again so the bugfix might have been pushed out to OpenShift already. Not too sure about that.
Nice to see a fellow stringer user here. :)