It works...
root@ante:~# umount /fotos/pinamar2011
root@ante:~# lvresize -r -L+10G /dev/mapper/fotones-pinamar2011
fsck from util-linux-ng 2.17.2
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This is an EXPERIMENTAL version of fsck.reiser4. Read README first.
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Fscking the /dev/mapper/fotones-pinamar2011 block device.
Will check the consistency of the Reiser4 SuperBlock.
Will check the consistency of the Reiser4 FileSystem.
Continue?
(Yes/No): Yes
***** fsck.reiser4 started at Mon Jan 30 06:31:01 2012
Reiser4 fs was detected on /dev/mapper/fotones-pinamar2011.
Master super block (16):
magic: ReIsEr4
blksize: 4096
format: 0x0 (format40)
label: pinamar2011

Format super block (17):
plugin: format40
description: Disk-format plugin.
version: 0
magic: ReIsEr40FoRmAt
mkfs id: 0x575b0492
flushes: 0
blocks: 237240320
free blocks: 11816468
root block: 207803654
tail policy: 0x2 (smart)
next oid: 0x82aa6
file count: 469669
tree height: 5
key policy: LARGE

CHECKING THE STORAGE TREE
Read nodes 25215
Nodes left in the tree 25215
Leaves of them 17901, Twigs of them 7220
Time interval: Mon Jan 30 06:32:06 2012 - Mon Jan 30 06:34:06 2012
CHECKING EXTENT REGIONS.
Read twigs 7220
Time interval: Mon Jan 30 06:34:06 2012 - Mon Jan 30 06:34:08 2012
CHECKING THE SEMANTIC TREE
Found 469669 objects (some could be encountered more then once).
Time interval: Mon Jan 30 06:34:08 2012 - Mon Jan 30 06:34:13 2012
***** fsck.reiser4 finished at Mon Jan 30 06:34:13 2012
Closing fs...done

FS is consistent.

Extending logical volume pinamar2011 to 915.00 GiB
Logical volume pinamar2011 successfully resized
fsadm: Filesystem "reiser4" on device "/dev/dm-10" is not supported by this tool
fsadm failed: 1

Well it doesn't...
:(