I remembered something. Install another theme, activate the plugin and get back to my Responsive theme. I tried with Twenty Twelve v1.1. Nothing. It does not solve the problem.
"Plugin could not be activated because it triggered a fatal error."
STEP 2 / Solving the problem
I made the export tables (Export). I wiped the tables (Drop). Activate the plugin. That went without any problems! Again I wiped the tables (Drop). I imported my old (Import).
Plugin work again!
Tables (original) are latin1_svedish_ci. It would be better to have utf8_general_ci which supports unicode. It seems to me that I've caused a problem because I have previously changed it and forgot about it.
On my SQL database is now again utf8_general_ci.
Raj, please, can you help me with this. I have a few questions:
(1.) Why does the WP Autoresponder not use utf8_general_ci? All other plugins have it.
(2.) Does it (utf8) soon can we expect?
(3.) Is it possible that this is causing problems for activation?
(4.) What to do now that this problem is not repeated at each deactivation / activation?
Thanks in advance