Bootcamp erased after upgrading to El Capitan

Hi, I have been following the steps of this thread:

El Capitan has deleted my bootcamp windows partition

which I was able to do until I reached the point of using gdisk to write the new partition requirements from the testdisk results. I get the following error:

Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING

PARTITIONS!!

Do you want to proceed? (Y/N): y

OK; writing new GUID partition table (GPT) to /dev/rdisk0.

Warning: Devices opened with shared lock will not have their

partition table automatically reloaded!

Unable to open device '/dev/rdisk0' for writing! Errno is 1! Aborting write!

I hate to clutter this forum with repetitive questions but I can't seem to find the answer to this one. Any help would be appreciated!