We had a situation wherein a colleague was attempting to get DB Links working. This was on a 11.2.0.4 database where password obfuscation is not allowed and the users were unsure of the passwords. After multiple changes to the passwords on the target system and drops and recreates of the links, the users continued to encounter errors while using the db link. We looked up a number of posts by different people on the web and then tried
alter system flush shared pool;
This resolved the issue. This was a non production environment. Please consider all the implications before you issue a flush in a production environment.
