blanc page with big attachments

Hi!

I'm using Roundcube since several months. Since the last update I've got a problem with big attachments (about 4 MB). When I try to open a mail with a big attachment I can only see a blanc page.

In the apache logfiles the following entries can be found: [Wed Feb 28 10:03:48 2007] [error] [client 84.57.181.181] PHP Warning: Cannot modify header information - headers already sent in Unknown on line 0, referer: https://webmail.widdix.de/?_task=mail [Wed Feb 28 10:03:48 2007] [error] [client 84.57.181.181] PHP Warning: Cannot modify header information - headers already sent in Unknown on line 0, referer: https://webmail.widdix.de/?_task=mail

Can anybody help me with this problem?