The error basically means that a synonym exists in the database that points to another object in a circle.

In one case, the error occurred while either dropping an existing table (with a synonym), or creating a table, when a synonym currently exists.

The answer is to "drop" the synonym from the database before dropping the table.  Here is a sample of the synonym drop command:
DROP {synonym name};

If the synonym is not owned by PBDS, you might have to search for the synonym under "ALL USERS" in the PL/SQL's Object Navigator to find its full name.  For instance, "PUBLIC.{synonym name}".  In that case, you can either drop it in PL/SQL by Right-Clicking on the object and clicking on "Drop", or use the full name in the Drop command (as listed above):
DROP PUBLIC.{synonym name};