problem with php script

Hello everyone I have a problem with this php script that gives this error *Fatal error*: Unsupported operand types in */usr/local/www/data-dist/brisk/php/classes/PageContent.php* on line *64 here is the part of the code that gives the error $this->currentWebPageCount += 1; $this->previousPage -= 1; This code is contained in a class called testPage and this class extends another class in a file called PageContent. the currentWebPageCount is initalized from a HTTP_GET_VARS['rows']; and I also check to see if it has been initalized with a isset() function. If anyone can help thanks *