Activating Context Layouts should not make the blocks reaction disappear

Check your PHP version. I was getting the same error. Through the course of debugging realized that my PHP version was 5.2.13. D7 minimum requirement is PHP 5.2.5, with 5.3 recommended.

Changing my PHP version to 5.3 fixed this for me, block contexts now show.

Is the Context Layout module enabled? This seems to disable the blocks reaction.

Not a sysadmin but i think that's the problem (PHP-FPM 5.2.17).

There is no reason why Context Layout should make the blocks reaction disappear from the list.

Doesn't Context Layouts put its stuff in the block reaction? If the blocks reaction disappears, doesn't that render the Context Layout unusable? Maybe the priority for this issue should be raised.

I'm having this issue and I'm using PHP 5.3.4.

I have the same issue. However, my web host said they won't be upgrading to PHP5.3 anytime soon. So I was wondering if there are any patches for this?

Regards,
Sherwin

There seems to be little activity on this bug. I successfully reproduced it on a fresh D7 install, so I'm bumping this to critical to try and get more attention for it.

Also when I deactivate Context Layout, Blocks Reaction shows up, but nothing shows on the right side boxes (settings area) when I select a Condition or a Reaction.

I encountered this problem today too.

I'm having this problem too, but cloning context (april/24) with git and clearing the cache fixes the problem. The only problem is that I have to do this manually or via drush. I'm creating a distribution and adding drupal_flush_all_caches(); at the end of the profile install doesn't solve the problem so this is still an issue for me.

PHP version is 5.3.2 using MAMP.

I had the same issue with a fresh install of D7. I had enabled context layouts and still couldn't see the block reaction. So, I changed my PHP version from 5.3.5 to 5.2.17, cleared the cache and it's now working properly.

Tested against core 7.2, latest 7.x-3.x branch code and ctools 1.0-beta1 and enabling context layouts does cause the blocks reaction item to disappear. Clearing the cache appears to resolve the issue. I have not uncovered the root cause.

indeed fix was very simple. clear cache.

I've encountered this bug as well. Clearing the cache indeed worked, thanks for the tip.

then

Running on PHP 5.2.17, fresh install. Just clearing the cache solved the problem. :-)

Looks like this is a duplicate of #1297776: Blocks missing from reactions when context layouts is enabled.
A fix is suggested here