Hello,
I have installed the JP-Ultimate Template using the Extension manager -> upload and install the package file.
I get the message that the template was successfully installed.
I can also see the template in teh template manager.
But when I click on the template, in order to change some settings, I get the message :
"Internal Server Error. The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.
Apache/2.2.3 (CentOS) Server at www.immo-mvp.be Port 80

This problem does not occur with other templates.

Has anybody an idea of what goes wrong here.

Please check Requirements
PHP 5.3+
PHP Multibyte String support
PHP JSON support
PHP DOM XML support

If any of these requirements are missing you might need to contact your webhost and ask them to install or enable the needed extensions.

I have checked the requirements and the are all OK.
I have found something in the logs :
EACCELERATOR(9254): PHP crashed on opline 2053012669 of main() at /var/www/vhosts/immo-mvp.be/httpdocs/templates/jp-ultimate/warp/config/layouts/fields/table.php:164291500, referer: www.immo-mvp.be/administrator/index.php?option=com_templates

Any idea what this means?

Seems to be a problem with your installed php accelerator:
eaccelerator.net/

Disable it and try again.