Assume, There is a web project that work fine in IE8 and FF3+ but there is some java script error in IE7- and the only thing that you have to find the problem is just an error from developer toolbar in browser mode IE7 like this:
Expected identifier, string or number Persons, line 135713438 character 9
and of course there is no line 135713438 and your English is very bad :D
So what can you do?