Ban on UAE entry for African nationalities?

I've recently been offered (and accepted) a job with a company based in Abu Dhabi and my contract is due to commence August 1st. I'm a British national and my wife and daughter are both Nigerian passport holders.

Last week, the company sent me through a letter of sponsorship and associated documents to take to the UAE embassy in London, to make visitor visa applications for my wife and daughter. When we reached the UAE embassy, I gave the application form, all of our passports and the sponsorship documents to the consular officer at the visa window. Having taken a brief look, within 30 seconds, the officer returned everything and said that the embassy “is only issuing diplomatic visas” and we should apply for a travel document through Eithad. This is all contrary to the information posted on the UAE London embassy website.

I then called the Etihad office in London and was told that they (Etihad) no longer issue travel documents since they “could not guarantee they would be ready in time for the travel date”.

Neither the embassy or Etihad made any mention of a ban on entry to the UAE for Nigerians (or any other African nationality for that matter).

I received a call today from the MD of the company, informing me that they had been in contact with the immigration authorities in Abu Dhabi, who had told them that there was an “unofficial” ban on visas or travel documents for all African nationalities.

This all seems a complete nonsense to me, one of my wife's friends in Lagos was issued with a UAE travel document less than a week ago and the daily Emirates flight from Lagos to Dubai is running as full as it usually is.

Can anyone confirm a blanket ban on African nationalities travelling to the UAE?

Are there any alternative solutions whereby my family can join me in Abu Dhabi?

Thanks