Check your servers “free” memory, all the available memory may be tied up in cache due to copying files to/from your server
Create a file the size of your available memory or larger.
Then copy the file and then permanently delete both the original and the copy. (Delete from command line, use shift + delete, and/or empty the trash bin)
Now all available memory should be free 🙂
Script:
fsutil file createnew 2gb.txt 2147483648
copy 2gb.txt 2gb-2.txt
del 2gb*.txt