[Petya V4sechkin]

The_Immortal, как обстоят дела с вирусами на проблемной машине?
Не установлен ли там Avast, случайно?

[The_Immortal]

Petya V4sechkin, вирусов нема, как и Аваста.

Проблема была в этом - на данной машине сиё надо было отключить.
Либо использовать флаг -h у PsExec:

- On Windows Vista and later, if UAC is enabled, a process launched by psexec -- even when run from an administrator account -- must have its elevate token set in order to get full privileges. This can be done by passing the -h attribute in the psexec command line. ... - The other way around this that doesn't require changing the registry is to just add the -h flag to the psexec command. This tells it to run the command with the elevated token, which is equivalent to launching a process "as administrator" from the context menu