Solving problems sometimes involves peeling the layers one at time like an onion. This is reference to the onion in this relative obscure movie: Dark City [Spoiler Alert].
1. We analysed the installation log file and there was a problem with VCRedist so we hacked it out from setup.ini file. The workflow is noted here:
http://knowledge.autodesk.com/support/autocad/troubleshooting/caas/sfdcarticles/sfdcarticles/AutoCAD-2012-installation-fails-on-machine-with-NET-4-5.html
2. We then tried installation of again and this time, there was a 997 error:
...so I applied this solution:
http://knowledge.autodesk.com/search-result/caas/sfdcarticles/sfdcarticles/Install-Failure-Error-997-Overlapped-I-O-operation-is-in-progress.html
I then needed to update article to include 3 GUID values for AutoCAD LT for the security exception and get a better image of the registry.
We needed to use Orca on the following msi files: AcadltLP.msi. acadlt.msi, AcadltPS.msi.
http://knowledge.autodesk.com/search-result/caas/sfdcarticles/sfdcarticles/How-to-Find-the-Product-Code-for-an-Autodesk-Product.html
I also tweaked and improved this solution to use a MSDN site to get Orca.
3. AutoCAD LT 2015 finally installed! But when we launched it, there is a side by side installation error and this means we actually needed VCRedist installed, even though it was listed as installed in the Control Panel.
http://knowledge.autodesk.com/support/autocad/troubleshooting/caas/sfdcarticles/sfdcarticles/Error-The-application-has-failed-to-start-because-its-side-by-side-configuration-is-incorrect.html
4. I manually tried to run all the .exe files in the following 2 folders:
C:\Autodesk\AutoCADLT_2015_SWL_English_Win_64bit_dlm\3rdParty\x64\VCRedist
C:\Autodesk\AutoCADLT_2015_SWL_English_Win_64bit_dlm\3rdParty\x86\VCRedist
...and I got the 997 error again!
5. We needed to add the VCRedist GUID values to the security exceptions list. To get the GUID values for the VCRedist, we needed to use verbose logging to get the GUIDS for those products.
a. We needed to enable verbose logging. I tweaked and improved this solution by adding a note to use a Microsoft Fix It tool.
http://knowledge.autodesk.com/support/autocad/troubleshooting/caas/sfdcarticles/sfdcarticles/Enabling-verbose-logging-for-installation-issues.html
b. I deleted all the files in %temp% folder.
c. I ran the first .exe file noted here:
~\AutoCADLT_2015_SWL_English_Win_64bit_dlm\3rdParty\x64\VCRedist\2008SP1
d. I copied all the log files from %temp% back into the same folder for analysis later . i.e.
~\AutoCADLT_2015_SWL_English_Win_64bit_dlm\3rdParty\x64\VCRedist\2008SP1
e. I then repeat for each folder. i.e.
~\AutoCADLT_2015_SWL_English_Win_64bit_dlm\3rdParty\x64\VCRedist\2010SP1
~AutoCADLT_2015_SWL_English_Win_64bit_dlm\3rdParty\x64\VCRedist\2012UPD4
~\AutoCADLT_2015_SWL_English_Win_64bit_dlm\3rdParty\x86\VCRedist\2008SP1
~\AutoCADLT_2015_SWL_English_Win_64bit_dlm\3rdParty\x86\VCRedist\2010SP1
~\AutoCADLT_2015_SWL_English_Win_64bit_dlm\3rdParty\x86\VCRedist\2012UPD4
NOTE: The name of the .exe file for the folders are above are called: vcredist_x64.exe & vcredist_x86.exe.
f. I then just opened each of the log files generated and searched for "ProductCode". The result is the article below:
http://knowledge.autodesk.com/search-result/caas/sfdcarticles/sfdcarticles/What-are-the-VCRedist-GUID-Product-Code-Values-used-in-Autodesk-2015-products.html
g. Just add all the GUID's into the .reg file. Example is below for AutoCAD LT 2015 (3 GUIDs) + VCRedist (6 GUIDs). If you have this problem, just download the file below and rename .txt to .reg and then double click it to import it into your registry.
AutoCAD LT 2015Error 997 Registry Fix: SecRepWhtlst+VREDIST
As you can see, we applied many articles to solve one problem. I would like to thank the technical guru Jeremy Hanson for helping me on this case and Gary A Johnston for confirming that this worked.