The file manifest.xml does not exist in the solution package
Creating a SharePoint solution file (which is a cab file renamed to wsp), can cause problems if the size of the file would exceed the space on an 1.44MB disk.
1.44MB? What the…? The default values for makecab, which is used for generating the cab file, will prevent the creation of a valid cab file 🙁
Thanks to Eugene Rosenfeld for finding this one.