senior members plz help me.. same problem again

when i try to upload my sample work to send buyer and try to upload escel file in rar... an error msg shows
what can be issue is it my browser problem or window problem????
.iamge and JPEG etc file are uploading but excel or .rar not uploading..

this error shows
""the uploaded file does not have an allowed extension""

is any one also face same problem???