Content Delivery - Un-publish Error - tridion

Question

We have found a pretty strange issue in SDL Tridion 2011 Sp1 Hr 1 Content Delivery in that when we un-publish content the publishing will fail.
The fail is really weird. We have created two structure groups:
100 Example
400 Other
Each contains the same page types. Pages contain standard metadata (text fields etc)
If I un-publish 100 Example on the SG all files are removed
If I un-publish 400 Other on the SG the publish task fails (CD log snippet below)
If I go into the 400 Other SG and select all files to un-publish, this is fine
The SG items contain no SG, or weird chars in the 'directory' name.
I see there is a hotfix - 'CD_2011.1.0.79212 - Cumulative hotfix' which is referenced in this SDL Tridion forum post (https://forum.sdltridion.com/topic.asp?TOPIC_ID=7554) - but the version number strikes me as SDL Tridion 2011 Sp 1.
I've installed hotfix CD_2011.1.1.83475 (a Cumulative Hotfix), but this doens't resolve the issue.
I didn't raise this with SDL support yet as I wanted to put this info out to the community first.
My error message is:
Unable to store item inside current transaction, Unable to remove data
entity, Unknown entity: com.tridion.storage.ItemMeta_$$_javassist_26,
Unknown entity: com.tridion.storage.ItemMeta_$$_javassist_26, Unable
to remove data entity, Unknown entity:
com.tridion.storage.ItemMeta_$$_javassist_26, Unknown entity:
com.tridion.storage.ItemMeta_$$_javassist_26 for transaction:
tcm:0-24997-66560 2013-02-05 15:10:18,660 ERROR DeployPipelineExecutor
- Final attempt in Phase: Deployment Prepare Commit Phase failed for transaction: tcm:0-24997-66560 2013-02-05 15:10:18,661 ERROR