I found that a server I needed to expand the disk on used IDE, had no time to convert it, so used the vmkfstools in shell to extend the disk, worked like a charm and server is up and running with the resized disk.
My problem is that I cannot see the new size of the disk reflected on the webinterface or vCenter. (Still says 40Gb resized to 55Gb)
Have I messed up or is there a fix to get vCenter to see the correct size of the disk again?
Command used: vmkfstools -X 55g <diskname>.vmdk