Hello Giulio,
a quick check in the TS database with MSE_CONTACT_TOLERANCE_FACTOR as keyword revealed that setting this environment variable was used a workaround in Creo Elements/Pro 5.0 to counter an issue where thin surfaces have been falsely recognized as interpenetrating, causing endless processing. Since this error has been fixed with Creo Parametric 1.0, the environemnt variable probably has been removed.
See CS6933 : A static analysis is not completed as expected in Creo Elements/Pro Mechanica
http://support.ptc.com/appserver/cs/view/solution.jsp?n=CS6933
Gunter