i have never heard of this "downgrade-dir-655.rar". Where did you get it from?
you can downgrade your dir-655 from 1.33NA if you dont like it using this method, This Has Been Tested BY ME & IT WORKS! "Downgraded from 1.32NA" to 1.21
1. download this modified dir-655 russian firmware (dont worry it's completly english! its also safe)
http://depositfiles.com/files/qarqeqmft
2. download the dir-655 firmware v1.21
ftp://ftp.dlink.com/Gateway/dir655/Firmware/
3. Disconnect your router from the internet (unplug the cable!)
4. enter your DIR-655's setup, Go To Advanced -> Firmware -> And Select DIR655A4_FW131RUB10.bin
then wait
5. After that your firmware should say 1.31RU on the right top in your router's setup.
6. Upgrade firmware again to the 1.21 firmware you downloaded. REMEMBER : Only after you applied RUSSIAN FIRMWARE you can upload 1.21
After upload, your DIR 655 will have the 1.21 very stable rom

You can also find the old shareport utility at ftp://ftp.dlink.com/Gateway/dir655/Apps/