When I enable page cache-plugin for joomla I can only download attachements once. If I click a second time on the attachment-link I only get a blank page. I am seeking a solution for this so I can use the cache-plugin together with k2.

Hello,
The blank page indicated a PHP Fatal Error.

Please enable error reporting and set it to maximum in order to see the actual error.

It is still blank even if error reporting is set to maximum.

Can you look at your error_log ?
Your hosting provider might assist you on locating it, if you do not know its location.

Nothing in the error log, but the server gives a 304 response.

GET /xxxxxxxx-xxxxxxxxx/item/download/149_cb2d60633d582163a9ce8e7b00819eb6 HTTP/1.1" 304

httpstatuses.com/304

Which caching plugin are you using? Joomla!"s native page cache or a 3rd party one?

Joomla!"s native page cache.

:-)

Is the caching plugin enabled?

Not sure what you mean, but for the moment the native page cache plugin is disabled since it gives a blank page when second time clicking on an attachment-link just gives the blank page and server reports 304 error.

I had browser cache enabled inside the plugin, and when I disable that the problem seem to be solved. I tried that when writing this so I will have to wait and test before I am 100% sure. It would of course be nice to have that enabled, but if works this way it is ok.

Actually, that is what I meant.
Joomla! caching plugin.

Let me know on your findings. With page caching disabled is the issue resolved?