Is the job in verify status, when it asks for the tape? if yes, it really does not need the next tape.

Thanks

Does it want the first tape back again so that it can write a line to indicate which tape comes next?

That would make sense!

I assumed that it was going to keep writing to that tape.

Excuse my ignorance : {

For the media set that both tapes belong to, did you set the overwrite protection period to a a period of time?   Otherwise, the tapes can become overwriteable immediately after they are used.

Also, check your Media Management Options (go to Tools ----> Options ----->  Media Management).  If it is set to the second option, Overwrite recyclable media in the media set before overwriting scratch media, then what you are experiencing is as expected.

If the above two conditions are present, your "Week4a" is used and it becomes part of a media.  However, the media set overwrite protection period is set to 0 hours, then it becomes overwriteable immediately.  If your Media Management Option is set to Overwrite recyclable media, then it will be asked for first before "Week4b" tape which is still a scratch tape.

You might want to read the following documents

http://seer.entsupport.symantec.com/docs/299050.htm

http://seer.entsupport.symantec.com/docs/192265.htm

which will explain the various media set settings better.

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If this clears up the mystery, please mark it as the solution. 

Yes... verify is turned on so this must be what it was.

The media is overwritable, and the options look for scratch before recyclable media.

Thanks again,
Meg