Target file is missing or wrong size error

Hi after hard drive drive problems of my download directory but not the system drive so dc program was unaffected so expanded my nas to now instead of just store some files to store all my downloads and then noticed very slow hashing 40s meg speed even though the nas array is capable of high 180s meg on copy so i guessed it would hash at over 100meg like did with usb3 drives on computer as before but than only a minor annoyance but now while hassling I thought i would starts some file downloading i set the download directory to a folder on the nas but all file from 10+ people wont download they start ok so it not networking problems as thats not changed but after a few seconds they stop and come up with target file is missing or wrong size error then go back to idle then when they retry come up with the same error. Ive even tried to set the download directory to the physical hard drive and same error even when deleting the download files and re adding then same error . Please help thanks