After a search line by line inside the .htaccess file by the method try and error, commenting and uncommenting the lines.
I can say this 4 lines are my error 500
#On
#RewriteBase /
#RewriteRule ^images/(.*)\.png$ /wp-content/plugins/anyfont/img.php [L]
#</IfModule>
The 4 lines are commented as I have them now to avoid the problem.
Seems to me plugin anyfont is causing the problem in some way.
For my is the end of the way cos im not a coder.
Sorry for the very bad english.
