usb flash drive reads fail

Hi, I am running stock netgear sw (latest release)on a refurbed wnr3500l. Usb Flash drives are recognized as to size and name/directories etc but reads for larger file sizes (> 100k) xl,word etc fail with read errors. The same drive can be taken to a laptop/desktop and all files read ok. 

The netgear share screens populate ok with drive info but once a read error occurs, the drive must be unmounted and remounted to access  share info again.

Any help appreciated.

Thanks