E: Internal Error, Unable to parse a package record

[Albert Cervera Areny <albertca@jazzfree.com>]

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Fetched 3608kB in 2m32s (23.7kB/s)
Reading Package Lists... Done
Merging Available information
E: Internal Error, Unable to parse a package record

update available list script returned error exit status 100.
Press <enter> to continue.

I'm using debian unstable and more than a week ago started appearing this 
error each time I update using dselect. The list (in select) isn't updated 
but when I choose 'install', the updated packages are installed. 

I tried to find what source was producing this error and it is the 'main' 
section. From the official debian http server and from the spanish one (both 
produce the same error). But if I take it out from sources.list the merge 
runs without problems.

Any ideas on how to solve this?
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