Once you get back from the Dusk/Dawn Towers to give Elena flesh, do everything you need to do first (store, buy, sell items; BE SURE TO GET RID OF YOUR FLESH! I only had it not work once and it was when I had flesh with me) and then save.
After you save, go back to the Wii Menu ( I accessed the menu by using the HOME Menu) and load the game again from there. Access your save on the game's main screen. Once it loads you back in the Observatory, immediately go to the place outside that lets you access the towers.
*BE SURE TO FOLLOW THIS AND TAKE YOUR TIME!! This might sound silly and tedious, but bear with me.
Once you are standing there, just stand there a few seconds (I count to seven seconds), then press the A Button to access the Tower List. Hover over the Dusk/Dawn Tower of your choice BUT DO NOT PRESS ANYTHING FOR 7 OR SO SECONDS! After 7 seconds, press A to get the confirmation screen. WAIT AGAIN FOR 7 SECONDS. After that, hit A and it should let you in.
For the 7 seconds, I just had the light on the options go back and forth 7 times as my timer
So, in short, anytime you need to go back to those towers:
1) get rid of all flesh and save
2) load the game again from the Wii Menu
3) stand outside the observatory in the Tower Select area and wait 7 seconds then press A
4) Hover over the Dusk/Dawn Tower of your choice and wait 7 seconds then press A
5) Hover over the enter tower option and wait 7 seconds then press A
