Failing to convert to PDF when called from web application (IIS)

I have tested my implementation via a console application and it works okay, PowerPoint launches to convert a .ppt to PDF and succeeds.
However, when using the implementation as part of my web application, i get the following error.

IIS App pool is running as NetworkService, and I have manually created the directories listed in the error, and given permission to NetworkService on the 2 Desktop folders but still getting the same error.

Any ideas how to go about this?

Also, as a possible solution, I would like to know if there is a way to force the use of the virtual printer, as if Office is not installed on the machine, even though it might be installed.

`
Error while converting C:\WINDOWS\TEMP\da28f32b-0b76-495c-bed9-e307771c1997.ppt to PDF. (Exception:
Message: An error occurred while converting the file.
Detailed error:
Error creating a new PowerPoint application instance.
Code: PDFTRON_UNKNOWN (-2147024891)
File: “PowerPoint.cpp”:62
Log:
Start check system account.
Session ID is: 0.
Failed to create Desktop folder in SystemProfile. boost::filesystem::status: Access is denied: “C:\WINDOWS\system32\config\systemprofile\Desktop”
Failed to create Desktop folder in SystemProfile. boost::filesystem::status: Access is denied: “C:\WINDOWS\SysWOW64\config\systemprofile\Desktop”
Done checking system account.
Creating a PowerPoint application instance.

Conditional expression: false
Version : 6.7.1.58328N
Filename : Convert.cpp
Function : trn::PDF::Convert::ToPdf
Linenumber : 1692
)
`

To force on the virtual printer call

`
PDF.Convert.Printer.SetMode(Convert.Printer.Mode.e_printer_only)

`