You sometimes may recieve the error below when trying to do stsadm -o addsolution -filename "wspname.wsp"
An object in the SharePoint administrative framework, "SPSolutionLanguagePack Name=0 Parent=SPSolution Name=il.sharepoint.workflows.wsp", depends on other objects which do not exist. Ensure that all of the objects dependencies are created and retry this operation.
wspname.wsp: The Solution installation failed.
This is especially the case if you have just done a retract/uninstall and you try to add straight away. If you try again in a few seconds it will work. Basically this is because when you delete a wsp from solution management and then immediately run this stsadm command, there will still be clean up operations going on in the background. So just leave a slight delay between uninstall of solution packages and re-deploys.