Upgrade from SugarCRM 6.5.2 to SuiteCRM

Hello !
I’m new here, thank your in advance for your time.
I wanted to try to upgrade a SugarCRM installation to SuiteCRM and i have an issue, maybe someone can help.
I tried to find some answer in the forum, but i didn’ find anything that match my problem.

So i have a SugarCRM 6.5.2 installed on a windows SQLServer (i tried a new install of suiteCRM and it works).

I have modified the php.ini file like that :
max_execution_time - > 6000
post_max_size -> 60M
upload_max_filesize -> 60M
max_input_time -> 200
memory_limit -> 256MB

When i tried with the assistant the package SugarCE Migration 6.5.x to Suite 7.1.8 it says : not compatible with your version 6.5.26
So i tried the SugarCE Migration 6.x to Suite 7.6.6 package, and after the upload of the file, i have an error 404.

Do you have and idea why i have this last error ?

Thank you for your help, and sorry for my english, i’m not a native.