Recently i got this error while updating the WSP's using powershell command Update-SPSolution commandlet.
following step i executed to fix the issue
1.Checked the solution store(Central Administration-->System Settings--> Manage farm solutions) and saw that the solution I was updating was not deployed and thrown error. The error it gave was not able to do GAC diployment of the dll. So i went to GAC and uninstall the WSPs related dlls and deployed the wsps again from central admin.
2. From services.msc I stopped and restarted the SharePoint 2010 Timer service and the SharePoint 2010 Administration service.
3. Then i ran the power shell command again. this time the WSP got updated.
Hope this help , while any one of you face this issue.