Oracle Solution for Error ora-30015

ORA-30015: previously offlined undo tablespace 'string

' is still pending

What triggered the Error:

the current operation is not allowed because an undo tablespace containing active transactions is pending from a previous SWITCH UNDO operation. The operation will be allowed again after all transactions in the previous undo tablespace are committed.

What should we do to fix it:

Wait for all previous transactions to commit before reissuing the current statement.