Hi Emilio,
The problem is that everything but a space (or other whitespace) will be matched with %s:
http://www.tcl.tk/man/tcl8.4/TclCmd/scan.htmM12
So you'd need to be able to specify a character class that doesn't include the in order to use scan for the first string. If you just want to split the string on a specific character you can use getfield or split instead:
http://devcentral.f5.com/wiki/default.aspx/iRules/getfield
http://www.tcl.tk/man/tcl8.4/TclCmd/split.htm
If neither of those options work, can you give more detail on what you're trying to parse? The more examples, the better.
Aaron