From Oracle FAQ
ORA-30678: Too many open connections.
What causes this error?
A connection to a remote service failed because your Oracle session already opened too may other connections.
For example, a UTL_SMTP.OPEN_CONNECTION() to a mail service may result in this error if the connection is not properly closed (UTL_SMTP.QUIT).
How to fix it
Reconnect to or retry after closing some of the connections.