I had exactly the same problem with SP2 for Inspire. I also had installed a pre-release of Inspire.
I uninstalled this pre-reliese and tried again to install SP2. Error 2705 appeared again.
After a lot of trays I found a solution:
1. Uninstall everything about Arcgis for inspire (pre-relieses, SPs etc.)
2. Make a fresh installation of Inspire 1.0.0
3. Install SP1 of ArcGIS for Inspire!
4. Install SP2 of ArcGIS for Inspire!
Yes, it seems that it needs to install SP1 before installing SP2!
Please read carefully the installation guides as you need to follow some more steps to actually "apply" the installed SP2!
I hope this will help someone ..