I had the error message "Cannot start sandboxed service RpcSs" in 3.44.2 so I upgraded to 3.45.08 but I had the same error message. Also I had an Access Denied message in 3.45.08 no matter what I tried to run.
As it turns out this is because my computer configuration had changed and my Sandboxie config is very restrictive, as I block HarddiskVolumes. (ClosedFilePath=*Device\HarddiskVolume4*)
I had changed my disk configuration and as a result the drive that holds my sandboxed stuff was reassigned to a different volume number. Once I figured this out I fixed it.
Posted here in case someone else encounters this error and has a device blocking config.