Might be a problem with write permission on the filesystem where the IS is installed. Check the id you are using for the write persmissions. I guess you would already have tried reloading the packages and even bouncing the server.
There is one more solution, you might have import statements for the schema file, even if these files are not found, webMethods may return this error msg.
To clarify this poster’s message, The user of the PC on which wM was installed should be an Admin or atleast have write privileges. He might not be referring to Admin user for Developer session.
Hope.
P.S: Thought, might be useful to persons in future who are searching for inputs on this issue