Workflow management is not working if you change your admin folder to a location like /mysecurefolder/admin.
This is due to incorrect links in the head section of Workflow.aspx and WorkflowItem.aspx.
To solve this issue you have to change both css and javascript links from ../util/ to
<%=episerver.global.epconfig.rootdir%>util/
/René%=episerver.global.epconfig.rootdir%>