I hope prettymans short and concise answer was clear enough.

In other words, to be able to fetch from a cursor, that cursor must be opened. Once you close it, any subsequent attemp to fetch from that cursor will fail.

In your case it is very simple. The steps involved are:

1. You opened the cursor C1
2. You started your loop
3. You fetched first record from your cursor C1 (which is still open)
4. As the last step of this firs loop itteration you closed your cursor C1
5. You continued your loop with the second itteration
6. You tried to fetch a second record from your cursor C1. But this step failed, because that cursor is not opened any more - you've closed it in step 4 above, remember?