CSV product importation stop on validation check

[Guiii]

Hello everyone,

i migrate my server few weeks ago, and now i can't upload any simple csv file, when i click on check data the loading icon appears but nothing else. on "system.log" i have this issue: 

2017-03-19T16:26:24+00:00 ERR (3): Notice: Undefined index: _root_category in /home/kilimcar/public_html/app/code/core/Mage/ImportExport/Model/Import/Entity/Product.php on line 654

the line referred:

$category = $emptyRootCategory ? null : $this->_categoriesWithRoots[$rowData[self::COL_ROOT_CATEGORY]]; 

I'm on magento 1.9.3.2 i hope someone have a solution, thank you in advance.

[Sinisa]

Open browser's developer console before you click on Check Data.

You will probably notice either javascript error in console, or 4xx or 5xx error in Network Tab, related to ajax calls (XHR). Paste here what you find, it will help us to find the root cause of issue.