I have had this error through multiple versions. Currently on Release 9.0.1FP10 SHF315.
It's the same in Notes and Designer.
Right click on the workspace icon and choose Replication ... Replicate. Intermittently but on a regular basis you will get the error "unable to invoke program" and will be unable to replicate.
You then have to close Notes and re-open if you want to replicate.