It's more likely that you have some kind of card issue. It almost looks like 2 specmaps are being used because the blocks are not completely dark. They seem lighter than the ocean would be with no specmap.
cartrite

I can almost reproduce your problem by using an 8k spec texture and the file referred to in the VT ssc file. It would only load if the Specular Texture line was in the Alt_Surface ssc file, not the solarsys.ssc file in the data folder, while trying to use the VT. Even though the VT had a spec map in the alpha channel, the 8k specmap loaded too.
I'm not sure how this could be happening to you though.
cartrite

Stephen, would you be nice enough to kick my a##?
I completely forgot to comment out the specmap declaration in my earth ssc!

Now all is smooth and clean...

Please, forgive the noob I am...

BTW, as I was toying with spec maps, I went over an inverted one giving a nice plastic look to the mountains. This make me thought that one nice effect would be to include in a certain proportion the snow/ice coverage from the color map into the specmap. This way we would have as final result all snow/ice zones with a higher spec than what we have now...

Do you think it could be feasible?

Cool! This got my brain cells working again. They needed the exercise.
cartrite

I'm not sure. I noticed some of the rivers that have specular effects in the summer months look extra "almost too" bright in the winter months already.

If this is tried, you would have to add very little light in those areas. Only a very little light, I have 0x1f on the land areas in the ver3 landmask, will add a good deal of specular highlights to a normalmap. 0x1f is almost black. So any snow and ice info would have to be limited by that limit or it would look very weird. I've had a few complaints that 0x1f was too much. That's why my site also has a landmask with no residual light added.
cartrite

Anyway our planet looks definitively FANTASTIC. The only missing element in my config is a 64k cloud map. Someone already made one?

The biggest cloudmaps I know of are only 32k. These are actually scaled down a little to conform to a power of 2 size. That's that old cloud map that came out with the older Blue Marble. I've even seen that one on the History channel. Makes me wonder if the view was captured from Celestia.
cartrite

Stephen, I'm unable to locate this file... do you know the link to it?

The raw files are here. http://mirrors.arsc.edu/nasa/Blue_Marble_2002/
Look for the cloud files. There are 2 of them ( East and West ) in png format and they are about 400 MB total. These are raw files and probably can use some work.
cartrite

Tx!
Stephen, last question. I have some huge discrepancies between my fresh VT and Cham's volcanoes location. Do you have such problem or all is fine for you? (I fear I have some kind of problem with labels...)

Stephen, forget the location stuff, apparently for a reason quite mysterious labels on my config are a bit odd... I must dig what can be wrong...

I gave a quick look and the volcanoes on the Pacific coast of N. America looked OK. I think rotation methods can throw off locations. There are several choices now. Uniform, Custom, Precessing, etc.
cartrite

Stephen, all is ok with the locs, I just had oblateness ON...

I peep into this 32k cloud map, it is really interesting because it match the continents etc, but hell it needs a ton of work to get it in good shape! Will try to do it little by little...