If the amount of data you are attempting to encode in a barcode exceeds the barcode's data capacity, the barcode will turn grey.
Thank you Steve..
Your PDF form should be published as a reader extended pdf
for more info refer Reader extension
I have the same problem as Raja. And it does not help to reduce the amount of information in the barcode. The barode field stil turns gray in Adobe Reader 9.
The strange thing is that there are no problems when I open and fill out the form in Adobe Reader 7.
I found the answer i another thread.