Can not allocate log, archival required

[jmodic]

I assume you have automatic archiving enabled for your database.

Have you checked the disk space on your archlog destination? It might be full. If so, make some room in it and archiving will continue.

If this isn't the case or if emptying the archlog destination doesn't help, try the following:

ALTER SYSTEM ARCHIVE LOG STOP;
ALTER SYSTEM ARCHIVE LOG START;

In any case, you won't loose any data becouse of this error. In fact, this error actually prevents you from potentialy loosing data in case media recovery will be needed in the future....