I've managed to fix this cab release by deleting all the release.dat files and then running a script I have written to re-reate them (following the same format as Dell). Place it alongside the root folder (in this case 990) and run it.

@ECHO OFF
setlocal enabledelayedexpansion

for /f "tokens=*" %%c in ('dir *.inf /a-d /b /s') do (

set abspath=%%~dpc
call set "relpath=%%abspath:%cd%\=%%"
call set "str=%%relpath:\= %%"

for /f "tokens=1 delims=." %%d in ('echo %time%') do echo !date! %%d > "!relpath!release.dat"
echo !str! >> "!relpath!release.dat"
)

There is a patch for ConfigMgr that addresses the root cause of the import failures on duplicate drivers (the reason for the release.dat files). You should look at using the patch unless you leverage categories heavily as the patch doesn't handle categories correctly.

Dell recommends that you do not import entire cab files into the ConfigMgr driver store and it adds to the complexity of driver management along with the importing issues.

Create driver packages directly from the extracted cab files and you will see that updating those driver packages becomes a very simple exercise without any importing issues.

I have a video that describes this process here http://www.delltechcenter.com/page/Client+Deployment

I did install KB2213600 when the cab files didn't import correctly, however, that just generated a different error. I don't remember what it was exactly as I have since uninstalled the patch, but it was something along the lines of 'general error' when importing the graphics drivers.

I didn't realize that the patch created more issues. I guess that's just more reason to look at creating your driver packages without importing. :)