"No credentials are available in the security package" when connection to Oracle is performed
Same problem here. Today I reopened a console application started in august and Oracle gave me the same exception.
Solved switching back to version 12.1.22 of Oracle.ManagedDataAccess from NuGet.
UPDATE 2016-12-27
Found final solution here: https://community.oracle.com/thread/3972810 The problem is caused by SQLNET.AUTHENTICATION_SERVICES set to NLS.
To solve the problem you have to edit app.config / web.config:
<oracle.manageddataaccess.client> <version number="*"> <dataSources> <dataSource alias="SampleDataSource" descriptor="(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=localhost)(PORT=1521))(CONNECT_DATA=(SERVICE_NAME=ORCL))) "/> </dataSources> <settings> <setting name="SQLNET.AUTHENTICATION_SERVICES" value=""/> </settings> </version></oracle.manageddataaccess.client>I added the <settings> section.