When using a database link that goes through Oracle Gateways to another vendor database (like SQL Server) you might get an error in SQL Developer that says “Bigger type length than Maximum”. Apparently this is a bug in thin JDBC driver. Workaround is to use thick/OCI driver. Select it in preferences and use TNS to connect to your database and it should work fine.
And just a reminder that SQL Developer needs Oracle 11g driver for this to work.