TYPO3 Core

When you click on "Media" in backend, the "Processing" message apear and never disapear. The media array is empty. By checking ajax calls, I found than every action in the backend generate the following ajax error :

Oops, an error occurred!
No module "" could be found.

The ajax called is :
/typo3/mod.php?sEcho=6&iColumns=18&sColumns=&iDisplayStart=0&iDisplayLength=10&mDataProp_0=__checkbox&mDataProp_1=uid&mDataProp_2=fileinfo&mDataProp_3=name&mDataProp_4=title&mDataProp_5=tstamp&mDataProp_6=keywords&mDataProp_7=sorting&mDataProp_8=categories&mDataProp_9=usage&mDataProp_10=variant&mDataProp_11=permission&mDataProp_12=status&mDataProp_13=hidden&mDataProp_14=creator&mDataProp_15=creation_date&mDataProp_16=modification_date&mDataProp_17=__buttons&sSearch=f&bRegex=false&sSearch_0=&bRegex_0=false&bSearchable_0=true&sSearch_1=&bRegex_1=false&bSearchable_1=true&sSearch_2=&bRegex_2=false&bSearchable_2=true&sSearch_3=&bRegex_3=false&bSearchable_3=true&sSearch_4=&bRegex_4=false&bSearchable_4=true&sSearch_5=&bRegex_5=false&bSearchable_5=true&sSearch_6=&bRegex_6=false&bSearchable_6=true&sSearch_7=&bRegex_7=false&bSearchable_7=true&sSearch_8=&bRegex_8=false&bSearchable_8=true&sSearch_9=&bRegex_9=false&bSearchable_9=true&sSearch_10=&bRegex_10=false&bSearchable_10=true&sSearch_11=&bRegex_11=false&bSearchable_11=true&sSearch_12=&bRegex_12=false&bSearchable_12=true&sSearch_13=&bRegex_13=false&bSearchable_13=true&sSearch_14=&bRegex_14=false&bSearchable_14=true&sSearch_15=&bRegex_15=false&bSearchable_15=true&sSearch_16=&bRegex_16=false&bSearchable_16=true&sSearch_17=&bRegex_17=false&bSearchable_17=true&iSortCol_0=0&sSortDir_0=asc&iSortingCols=1&bSortable_0=false&bSortable_1=true&bSortable_2=false&bSortable_3=true&bSortable_4=true&bSortable_5=true&bSortable_6=true&bSortable_7=true&bSortable_8=false&bSortable_9=false&bSortable_10=false&bSortable_11=false&bSortable_12=true&bSortable_13=true&bSortable_14=true&bSortable_15=true&bSortable_16=true&bSortable_17=false&M=user_MediaM1&tx_media_user_mediam1%5Baction%5D=listRow&tx_media_user_mediam1%5Bcontroller%5D=Asset&tx_media_user_mediam1%5Bformat%5D=json&M=user_MediaM1&_=1369577066889