Basically on a clean windows XP machine, if you install AutoCAD 2011 (with SP1.1) and AutoCAD Civil 3D 2011 (with SP1). Then install SAP for AutoCAD 2011 and start either AutoCAD 2011 or AutoCAD Civil 3D 2011 and the programs will open fine.
However, if another user logs on the system and opens AutoCAD 2011 (or AutoCAD Civil 3D 2011), the program will open fine, but opening the second program will give profile error:
Unable to load profile file. Some profile information saved in last session may not be restored.
The program will open with missing GUI elements. It appears that problem relates to the fact that when you start AutoCAD 2011, it creates:
HKEY_CURRENT_USER\Software\Autodesk\AutoCAD\R18.1\ACAD-9001:409, will also creates HKEY_CURRENT_USER\Software\Autodesk\AutoCAD\R18.1\ACAD-9000:409 (which is for Civil 3D).
However in HKEY_CURRENT_USER\Software\Autodesk\AutoCAD\R18.1\ACAD-9000:409 has has only one entry, related to DWG Converter. If you reverse the order of launching the application (e.g. starting with Civil 3D and then open AutoCAD) than C3D reg keys are created correctly, but AutoCAD does not. The profile error occurs with the second application regardless of the order of launch.
The workaround for this issue is:
1. Start AutoCAD 2011.
2. Open the Registry Editor (regedit).
3. Export HKEY_CURRENT_USER\Software\Autodesk\AutoCAD\R18.1\ACAD-9000:409\DwgConvert key.
4. Delete HKEY_CURRENT_USER\Software\Autodesk\AutoCAD\R18.1\ACAD-9000:409 key
5. Start Civil 3D 2011 and let Civil 3D 2011 create user profile related content.
6 Import DwgConvert key you exported in the step 3.
Thanks to Avto Chachava for this tip.