In Commerce Server 10.0, the staging project status is always shown as "Sent" and the error message "Failed to start project Your_Staging_Project_Name. It is already running." appears when trying to start a new Replication.
The staging service in Commerce Server 10.0 still tries to access a registry sub-key under a Microsoft key.
The problem has been fixed in Commerce Server 10.1.
As a workaround for Commerce Server 10.0, users can manually create the following registry keys and values allowing staging projects to be executed successfully:
On a 64-bit OS:
[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\CSS\ProjectDeploymentLog]
"PollingInterval"=dword:00001388
"ShutDownTimeOut"=dword:000007d0
"ThreadPriority"="Normal"
On a 32-bit OS:
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\CSS\ProjectDeploymentLog]
"PollingInterval"=dword:00001388
"ShutDownTimeOut"=dword:000007d0
"ThreadPriority"="Normal"