Dear Gottfried,
As I can see from exception file you've attached, exception is not
"positive number required
parameter name: bufferSize"
but
"Exception Message:
Invalid image file type: x-png"
Do you use some special images? Can you send an image or test rdl with the image of "x-png" type?
It seems that Mime-Type of image at least a little bit strange "x-png" and doesn't corresponds to standard types. We need example of image that you've used.
Also you should check out report source, may be in your report there is an embedded image with such x-png mime-type, which is not currently supported.
Something like
image/x-png
Anyway we are waiting for further information about this issue.
Thanks.