Added variable form DISM, since it sometimes wasn't found.

Also added verification check that DISM exists.

Windows/Install_dotNET_FrameWork_3.5.cmd

 : Specify path to \sources\sxs (for the right version of Windows 10)
 SET PATH="%1"
 
+SET DISM="C:\WINDOWS\system32\DISM"
+
 : Check that \sources\sxs exist
 IF NOT EXIST %PATH% GOTO :FAILED
 
+: Check that DISM exist
+IF NOT EXIST %DISM% GOTO :FAILED
+
 : Check that \sources\sxs\*netfx3* and \sources\sxs\*NetFx3* exist
 IF NOT EXIST %PATH%\*netfx3* GOTO :FAILED
 IF NOT EXIST %PATH%\*NetFx3* GOTO :FAILED
 
 : Install .NET Framework 3.5 (incl. 2.0 and 3.0)
-DISM /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:%PATH%
+%DISM% /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:%PATH%
 GOTO :END
 
 :FAILED