I guess this info is from alert file. Check to see how many archive processes you have. If you have two or more, the missing archived file should be in the other archive process log(BACKGROUND_DUMP_DEST). Check to see if the archived log is really missing. I don't think so.
1 All Members of the redo log are in the same disk.
2 You might have configured Hardware Level Disk Mirroring and duplexing of redo log files.
Basically when a redo log gets filled up, Oracle informs the ARCH process to do archiving the completed redo log file. Then the ARCH process tries to read other member of the redo log group, but it was not filled, because OS still writing the data into redo log file (2nd member).
How to eliminate:
1 If hardware level mirroring done, then you do not need duplexing of redo log files. You can drop the 2nd member in each group.
2 If you still need software level mirroing of redo log files, place them in the internal disk.