I had the same problem with a Galaxy Tab 2 7.0 (P3110) and have fixed it.
After successfully flashing CWM, any time I entered download mode the 'NO COMMAND' came up and the recovery was basically useless (showed the lying down android with red triangle in the background).
Found solution on a Galaxy S4 forum but it worked for my Tab 2, and probably some other devices.
SOLUTION:
1) Flash CWM as normal, except untick 'auto reboot' before you press start.
2) Once it's finished, unplug USB and power off directly from the download screen (just hold the power button in).
3) Next try and enter recovery mode, and if you're as lucky as me you'll get into the custom recovery and not the dodgy stock recovery.
The original forum was for Galaxy S4, so said to take out battery once the flash was complete. Tab 2 has not got removable battery, so I had to improvise by just powering off.
Hope this helps anyone in same situation as I was about half an hour ago.