500 Internal Server Error after frontend login

[anna_w27]

Joomla 2.5.16
Virtuemart 2.0.24c

I have the following problem. When I login at the frontend of my website, it gives a 500-internal server error in Internet Explorer and a blank screen in Google Chrome.
When I refresh the page a couple of times, it mostly works again.

When turning error reporting on, I get the following error:

Notice: Trying to get property of non-object in /modules/mod_virtuemart_login/tmpl/default.php on line 41 Notice: Trying to get property of non-object in /modules/mod_virtuemart_login/tmpl/default.php on line 42 Notice: Trying to get property of non-object in /modules/mod_virtuemart_login/tmpl/default.php on line 43

Any idea what this means?

[sadrem]

Hello,
Have You defined absolute path for tmp and log directory?
Message You get is not an error it's just Notice so it's not a problem.

[anna_w27]

Yes log and tmp directory is filled in correctly (abolute path)

Any other ideas?

[sadrem]

Whai is Session time seted in joomla?
What is hosting? 
check apache error log. It seems to me that problem lays in hosting. If not You must get every time error and not "refresh the page a couple of times, it mostly works again."

[anna_w27]

Session time = 300 (is it too high?)
My website is hosted at pcextreme.nl
And where can I find the apache error log?

[sadrem]

Apapche log must be under cpanel apache log, You can also ask hosting support where to find it and activate.
You have 2 apache logs : access log - not interesting , apache errors.
If You can attach apache will be helpful and provide link to Your site.
Regards.

[anna_w27]

I've send my hosting a message, and they told me I can't access the Apache error log.

The website link is http://www.brommobielsloperij.nl

I also think the problem doesn't occur all the time. Sometimes it works correctly :S