Can't re-use search code

I've serached and serached through the code but I can't find a reson for this ...

Search page, functioning
Name: inner16.php
Loaded by index3.php as an include
There are 4 search fields (2 text, 2 dynamic drop downs)
Loads a results page

Results page
Name: inner70.php
Loaded by index3.php as an include
At the top of this results page the search fields are repeated in a "search toolbar" and preloaded with the serach values
Everything working perfectly

1. If I repeat the code in page inner16.php inside another page, alos calling inner70 ast the results page, it doesn't work.
2. Ditto if I copy inner16 to innerXX and try again.
3. Ditto if I load the working page, inner16, as an include into a different index2.php page which is exactly the same!

I feel like there is a relationship between inner16 and inner70 that I don't understand - the common denominator is the index3.php file that uses these as includes. I cannot find the problem anywhere ... !!!

I can post code, but not here ...
THANKS