The definition of the task sequence (e.g. the specific steps to run) is distributed to the client using System Center Configuration Manager’s policy mechanism.  By default, clients are configured to download policy every 24 hours (this means that after you change the definition of a task sequence it could be up to 24 hours before it takes affect on the client).  We use this polling mechanism because it enables Configuration Manger to support a large number of clients with a relatively small number of servers.  However it can definitely make debugging task sequence a bit of a pain.  Here are some tips:

Option 1: Refresh Policy on the client

1. Make your change to the task sequence
   
2. On your client open the “Configuration Manager” control panel applet and run the “Machine Policy Retrieval & Evaluation Cycle” action on the Actions tab.
   
3. Wait 2 minutes while the policy is downloaded and processed
   
4. Run the task sequence
   

To make it clear that the client has received the new policy I sometimes change the name of the task sequence in step 1 to make it clear that new policy has been received.

Option 2: Use Boot Media

Unlike the Configuration Manager client, boot media (which can also be run in the full OS when a client is not installed) downloads policy every time it starts.  So, depending on the type of task sequence I am testing I sometimes find it convenient to use boot media.

Hope this helps.

Contributed by Brett Flegg