When editing an "Install Network MSI " action, if the file path is altered, an extra set of quotation marks is placed around the parameters.
n:\msi apps\adobe reader 9.msi
this will result in the MSI file being shown as
"n:\msi apps\adobe reader 9.msi"
and the install parameters as
/i "n:\msi apps\adobe reader 9.msi" /qn
(and similar results for the other 2 parameters).
Now make any small change to the MSI file name field (ensure that the space remains in the file name) and tab out.
Another set of quotation marks are added to the 3 parameter fields, so that in this example, the install parameters field is
/i ""n:\msi apps\adobe reader 9.msi"" /qn