Two more things to add to what I've said in my last message:
1) I didn't think about it at first, but actually, it would seem more likely to me that VP62 is a strain of XMRV that had undrewent more mutation than the Lithuanian strain - meaning, the Lithuanian strain, in my opinion (and while remembering that my knowledge here is little), is more likely to be an ancestor of VP62 than the other way around, and that is because:
Deletions remove one or more nucleotides from the DNA. Like insertions, these mutations can alter the reading frame of the gene. They are generally irreversible: though exactly the same sequence might theoretically be restored by an insertion, transposable elements able to revert a very short deletion (say 12 bases) in any location are either highly unlikely to exist or do not exist at all. Note that a deletion is not the exact opposite of an insertion: the former is quite random while the latter consists of a specific sequence inserting at locations that are not entirely random or even quite narrowly defined.
http://en.wikipedia.org/wiki/Mutation
So it seems to me that it's more likely that the Lithuanian XMRV existed before VP62, and that VP62 is a mutation of the Lithuanian XMRV. Now, look at the following theory: The Lithuanian XMRV existed in Lithuania before any type of XMRV existed in the USA. In at least one of the people infected with the Lithuanian XMRV, the virus underwent a mutation that caused the 15 base pairs deletion that we see in VP62 and the almost-identical sequences (like the WPI full sequences). That person then travelled to Nevada and infected a person from Nevada with that XMRV, which is like VP62. On another occasion, another person from Lithuanian - this time a person that is infected with the Lithuanian XMRV - travelled to Boston (the Lo/Alter study included 25 patients from Dr. Komaroff's clinic, which is in Boston - so I guess most of them were from the Boston area) and infected a person from Boston with the Lithuanian XMRV. That would even make some since, because Dr. Hanson had told us that the MLV-related viruses that she found in her Lyndonville (New-York) cohort are more like the sequences found by Lo and Alter then the sequences found by the WPI. And While Nevada is one of the places in the USA that is the most far away places from Boston or New-York, Lindonville (New-York) and Boston are relatively very close. So it would make more since when the highly identical sequences would be found in relatively close places, and a somewhat divergent sequences would be found in a reltively far-away places.
One must remember that this theory is simplified: You don't have to have just one person with a deletion in the Lithuanian XMRV, you can have many such people. And they don't have to travel directly to Nevada, they can infect someone from Britain, for example, and that someone might infect someone from the netherlands, and that someone might infect someone from Nevada. And you don't have to have just VP62 in Nevada - you might have also the sequences from Lyndonville, Boston or Lithuania - but you might have them in a lower number of people.
2) There is already at least 1 example (it's just the one that I know of) of a known mutation that the same gene in our body underwent, and still it is the same gene - and it's also more common in one place of the world (Europe) than in other places:
For example, a specific 32 base pair deletion in human CCR5 (CCR5-?32) confers HIV resistance to homozygotes and delays AIDS onset in heterozygotes.[44] The CCR5 mutation is more common in those of European descent
http://en.wikipedia.org/wiki/Mutation
So you see, here we have a 32 base pair deletion in a gene - but it's still called by the same name (with a subtype). Moreover, it seems that this subtype of the gene is more common in one place of the world (europe) than in other places - so it fits with the theory that XMRV VP62 is more common in certain areas of the world than in other areas. This might explain the negative studies: If the WPI test is sensitive enough, and can find viruses that are, for example, "just" 95% identical to VP62 (and also with mutations not just in one place, but in several different places accross the strain), it's possible that what they are finding in the UK is a mutation of VP62 (actually, as I've said, it seems to me that it's the other way around - that VP62 is a mutation of that virus, but who knows...), but they cannot know that because they haven't yet sequenced the full virus.
Anyway, it all comes back to one thing: That is why your test should be extremely sensitive; That is why you, at this time, should only use tests that were clinically validated (and if you think that they are giving false results - you should first try them, and then, if you think that the results are false, you should explain why, or even make experiments that would give evidence or proof that the results from these tests were false); And that is why, at this time, a scientist must keep an open mind and remember that had we known everything, we either had a cure to all of the diseases, or we would have known about diseases that no matter what one would do, it is impossible to find a cure for them. But we are not there yet, right?