When you try to run the cli upgrade tool (php upgrade.php upgrade) in 2.4.8.x and your php version is <5.3 you get an error:
Parse error: syntax error, unexpected T_FUNCTION in /var/www/localhost/htdocs/ojs-2.3.4/plugins/importexport/crossref/CrossRefExportPlugin.inc.php on line 210
The reason is that CrossRefExportPlugin.inc.php uses anonymous functions in a few places. Unfortunately, anonymous functions became available in php>=5.3
(I suspect that you will get similar errors when running a freshly installed OJS 2.4.8.x with php <5.3.)
So, please either change the php requirement in README file, or (preferably) change the relevant code… In the latter case, anonymous functions may be used in other parts of the code, so changes may be needed in other files too.