Fujitsu Siemens Raid Controller communication problems

Hello everyone,
I have just build a NAS with OMV. I am using a Fujitsu-Siemens D2516 C11 raid controller card in one of the pcie slots and have a raid 5 configured. Now everything seemed to work perfectly fine first. In OMV the raid 5 volume shows up as a single drive and I have successfully created a filesystem on it and even a shared folder. But every few minutes when OMV is trying to read or write to or from the raid volume it throws a communication error message. Clicking the 'Show Details' button just opens a text box that contains 'communication error' and nothing else. When I try to copy a large file to the raid volume it starts out very good, but at one point it just stops dead in its tracks and wont continue until it throws a random error message.
So I guess there is some sort of problem with OMV not properly recognizing the raid controller. Is there any way I can get this to work or would I need to buy a different raid controller or hba or even just use unraid or some other os?