I have just assisted in resolving this problem which got me some time ago. If you are developing a feature with a module and receive this error, it is because your module path is a folder and you are setting the "Type" attribute to "GhostableInLibrary".
<?xml version="1.0" encoding="utf-8"?>
<Elements xmlns="http://schemas.microsoft.com/sharepoint/">
<Module Url="_cts/Folder" Name="Modules">
<File Path="ModulesTemplate.dotx" Url="Template.dotx" Type="GhostableInLibrary" />
</Module>
</Elements>
If the "Url" attribute of the "Module" element points to a folder, rather than a list, then you cannot set the "Type" attribute to "GhostableInLibrary" as this is an attribute of a document in a library.
Great tip. It helped me. Thanks.
NLV