FOUND_ROWS() returns wrong result

Hi,

I've installed MySQL 5.0.27 on a LIVE environment while DEVELOPMENT runs a
lower version, yes I know wrong thing to do.
I've run into quite a few issues which are causing me lots of problems, the
main one being that FOUND_ROWS() return a wrong result.

The queries in questions are

SELECT SQL_CALC_FOUND_ROWS
PI.productInfoIdentity
, PI.productInfoTypeIdentity
, PI.productCategoryIdentity
, PI.dateStamp
, PI.documentIdentity
, PIT.productInfoTypeTitle
, PC.productCategoryTitle
, D.documentTitle
, D.documentIdentity
, D.originalExtension
, D.originalName
, D.fileSize
FROM tbl_productinfo PI
INNER JOIN tbl_productinfotype PIT
ON PI.productInfoTypeIdentity =
PIT.productInfoTypeIdentity
INNER JOIN tbl_l_productcategory PC
ON PI.productCategoryIdentity =
PC.productCategoryIdentity
INNER JOIN tbl_document D
ON PI.documentIdentity =
D.documentIdentity
INNER JOIN tbl_l_country C
ON C.countryIdentity =
PI.countryIdentity AND PI.countryIdentity = 1
ORDER BY PC.productCategoryTitle
LIMIT 0, 10;

Which returns nothing

Second statement
SELECT FOUND_ROWS() AS value;

Returns 8, which is completely wrong. The numbers returned do not make any
sense either, as I have others that should return 0, but return 6 or some
other number.

Any help would be much appreciated.