Transaction log reported full but is not
In all probability you had a large transaction that filled up your transaction log.  When the transaction failed it rolled back.  This cleared up your transaction log.

If that particular transaction needs to be processed then you can either


Modify your log size and max log size - This is best if this is a regular process.  Running a transaction log backup right afterwards is not a bad idea either.
Change the code to reduce the amount of transaction space needed.  This could be by using a minimally logged operation or by doing several smaller transactions (with a transaction backup in the middle).