This is an issue I'm not very informed, so I don't have a good in depth knowledge.
There is a national repository of information in Salamanca called Archivo Nacional de la Guerra Civil which is the main archive of documents about the Spanish Civil War.
Those documents were compiled just after the Civil War, thus, during Franco's Dictatorship.
Catalonian nationalists argue that the documents which had their origin in Catalonia should be returned to "their true owners" (creating an archive of that documents in Barcelona and thus dividing the repository).
Those are the facts. Now the politics.
Ten years ago the socialist government studied the issue as a way of having the support of CiU (catalonian moderate nationalists, if there has even been such a nationalist :p ). Experts (from both parts, central government and catalonian government) concluded that the archive should not be divided due to technical reasons (you may now, as a librarian, that repositories must be placed in only one place) to easy documentalists and historians their studies. Point.
Now ZP is in minority in the Parlament, and needs the support (mainly) of communists and ERC. ERC is the most radical extreme-left nationalist catalonian party, and seeks openly independence from Spain. In any other country this would be a paradox (a government supported by a party that seeks the destruction of the country). Not in Spain. Not for ZP.
Therefore, with a coalition of socialists + communists + catalonian separatists both in the government of catalonian autonomy and the central government, the issue has been rised again. And this time ZP has dialogued by imposing the division of the archive and moving a part to Barcelona. Salamanca citizens see this as an offense (since the archive is one of its main cultural values) and are protesting its movement.
Of course PP has taken advantage of this and has supported Salamanca authorities against the Government.
It seems that the "ultra-tolerant" Zapatero and his political partners are not very happy to have had 100,000 persons in the demonstration:
Josep Lluis Carod-Rovira (ERC leader):
"I will court PP for the insults in the demonstration to silence fascists. The franquist right of fascist culture uses menaces while we uses ideas and votes." Remember that ERC was the political wing of Terra Lliure, a terrorist band akind to ETA in Catalonia, and was the political party which supported at least two coup d'etats in 1932 and 1934 against the Republic with its armed militias.
Joan Puigcercós (ERC leader): "It is better for PP to organize demonstrations than organizing coup d'etats like they have done until now"
Carmen Calvo (PSOE Culture Minister): "We must not forget that there was a coup d'etat against the democratic Spain of the republican constitution...PP leaders don't understand Spain."
This is the kind of arguing of our governors. The thing is: who cares about an archive?
The problem is that the socialist government will give anything to ERC in exchange of its support, no matter how detrimental it is for Spain's interests.
Fernando