problem when upload file

[Itek]

Hello. I'm very regard if you help me to solve my problem
I changed my upload file size limit to 20MB in both admincp and php.ini files ( in root folder ).
It seem works well when i change this limit to 8MB but when i try to change it to 20 MB. When some one upload file , they have error:"Invalid $idname specified. If you followed a valid link, please notify the administrator". Now i don't know the reason.
Can you help me to solve it ?
Thank for your help

--------------- Added [DATE]1195137978[/DATE] at [TIME]1195137978[/TIME] ---------------

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