Data file on remote location(server) is not found, error generated in App Engine Peoplecode.

The issue is found during the testing for PS Tools 8.59 upgrade. The essence of the problem is that files located on a remote server are not found/detected and, therefore, not processed, error generated by Peoplecode looks like this:

"File <\\<File server or mapped drive letter>\DataFiles\Test\InstanceLocation\Data_Test.txt> is not opened or opened in wrong mode for method ReadLine. (2,627)"

Several different ways were used to define remote file location, i.e. "\\FileServer\DriveLetter$\DataFolders\" or "\\FileServer\DataFolders\" and result is always the same: the error above.

The same program (custom App Engine) with the same file location definition runs/completes successfully in PS Tools 8.57 environment.