I did what sh_kamalh sugested. For me it didn't work.
I used some commands to retract and remove the solution (look at help on "stsadm -help retractsolution" and "stsadm -help removesolution"). Then, I did someting a little different:
1) Use the command: stsadm -o addsolution -filename "<fullpath>\DP.Sharepoint.Workflow.wsp"
Where <fullpath> is the complete path to the wsp file.
2) I opened Central Admin, selected form the left menu "System Settings" and the I clicked on "Manage Farm Solutions" link.
This took me to a page that listed all my installed solutions. One of them was DP.Sharepoint.Workflow... and it stated that it was not deployed.
On the toolbar there is a link that reads "Deploy solution"... so I selected the DP solution, and then clicked on the link.
A new page opened where I could choose when and where to deploy the solution. Pretty straitforward.
3) After deployment through Central Admin.... I opened Sharepoint Designer 2010 and... voila!!! The actions where there!