memory issues when copying large amounts of data

Many times when I try to copy 500,000 data points array within Igor, I get the following error:

The operation could not be completed because Windows OS error - Access Denied.

I have Windows 7 x64, 4 GB of RAM. Is the problem simply lack of enough memory?
"Access Denied" typically relates to file and folder permissions, not to memory.

It would be a step in the right direction if you would state precisely what you do that leads to this error.
I have several 500,000 data-points wave, I simply copy one of them trying to append it to another, and the mere act of copying gives this error.
Yes I was doing it through clipboard. Are there commands to append a wave to another?