XF 1.5 Not able to import style XML's?

Hi, i was just wondering why i cant import any xml files to my xenforo, it promts me with this error
Please upload a valid style XML file.

and sometimes this error

Please enter a valid file name. The requested file could not be read.

i have tried multiple styles, but all have the same issue, installed xenforo many times, remade database many times.
any help would be greatly appreciated!