can't upload 2 WUs

I'm having problems to upload 2 certain WUs. When I start boinc, i get this message:

22.03.2007 06:37:29|Einstein@Home|[error] Couldn't find suitable URL for h1_0538.5_S5R1__1910_S5RIa_0_0
22.03.2007 06:37:29||[error] No URL for file transfer of h1_0538.5_S5R1__1910_S5RIa_0_0
22.03.2007 06:37:29|Einstein@Home|[error] Can't initialize file transfer for h1_0538.5_S5R1__1910_S5RIa_0_0
22.03.2007 06:37:29|Einstein@Home|[error] Couldn't find suitable URL for h1_0538.5_S5R1__1904_S5RIa_0_0
22.03.2007 06:37:29||[error] No URL for file transfer of h1_0538.5_S5R1__1904_S5RIa_0_0
22.03.2007 06:37:29|Einstein@Home|[error] Can't initialize file transfer for h1_0538.5_S5R1__1904_S5RIa_0_0

When I repeat the communication, I get this message:

22.03.2007 06:37:51|Einstein@Home|[file_xfer] Started upload of file h1_0538.5_S5R1__1910_S5RIa_0_0
22.03.2007 06:37:51|Einstein@Home|[file_xfer] Started upload of file h1_0538.5_S5R1__1904_S5RIa_0_0
22.03.2007 06:37:52||Project communication failed: attempting access to reference site
22.03.2007 06:37:52|Einstein@Home|[file_xfer] Temporarily failed upload of h1_0538.5_S5R1__1910_S5RIa_0_0: http error
22.03.2007 06:37:52|Einstein@Home|Backing off 1 hr 28 min 24 sec on upload of file h1_0538.5_S5R1__1910_S5RIa_0_0
22.03.2007 06:37:52|Einstein@Home|[file_xfer] Temporarily failed upload of h1_0538.5_S5R1__1904_S5RIa_0_0: http error
22.03.2007 06:37:52|Einstein@Home|Backing off 2 hr 24 min 54 sec on upload of file h1_0538.5_S5R1__1904_S5RIa_0_0
22.03.2007 06:37:53||Access to reference site succeeded - project servers may be temporarily down.

All other WUs have been uploaded w/o problems.
Can anyone help me?

Thanks,
Juergen Fricke