[4.27] Cannot generate source files

I am trying to switch version from 4.25 to 4.27 for some old project so I can get rid of the old version.

For some C++ projects I could only move to 4.26 as 4.27 showed me following error.

Running .../UE_4.27/Engine/Binaries/DotNET/UnrealBuildTool.exe  -projectfiles -project="...MapTests.uproject" -game -rocket -progress -log="....log"
Discovering modules, targets and source code for project...
While compiling ...\UE_4.27\Engine\Intermediate\Build\BuildRules\UE4Rules.dll:
error CS0042: Unexpected error creating debug information file '...\UE_4.27\Engine\Intermediate\Build\BuildRules\UE4Rules.PDB' -- '...\UE_4.27\Engine\Intermediate\Build\BuildRules\UE4Rules.pdb: Access is denied.
ERROR: Unable to compile source files.

I tried making the UE4Editor.exe as well as the UnrealBuildTools.exe to run as Administrator. That didn’t help, also unchecking “ReadOnly” in the folder properties for the whole folder didn’t help.

When changing to 4.26 it works, but I’d still like to move to 4.27 (or maybe later at some point).

Thanks in advance and cheers!