Undefine function json_decode

After installing v 0.9.1 i get this message with every browser I open my site:
Fatal error: (avytin) Call to undefined function json_decode() in .../plugins/system/mobilebot.php on line 40

With v 0.9 at least I did not have any problems in the version for my computer and the iphone version worked if no graphics were included.

Do you have any idea on what is causing the problem?

thank you!

Hi orbital,

Could you check from your phpinfo() if JSON extension is enabled? Thanks.

It is enabled and I get the error with version 0.9.2 as well. Could it be interacting with some other plugings?