new AM, best way to obtain new block at end of index?

Hi list,

currently I am obtaining a new block at the end of an index with:

buf = ReadBuffer(rel, P_NEW);

but it throws:

ERROR:  unexpected data beyond EOF in block 0 of relation base/11874/156053
HINT:  This has been seen to occur with buggy kernels; consider updating
your system.

system is up to date:
$ uname -r
2.6.35-28-generic

Is there another way to do it? What could be the source of the problem?

Yves