A link on the Government's website for former Afghan staff to apply for relocation is being affected by a "technical issue".
Links to both the Afghan Relocations and Assistance Policy (ARAP) contact and application forms are unavailable.
In an update on the web page, the Government says: "We're aware of a technical issue with the Afghan Relocations and Assistance Policy application form, which we are working to resolve.
"We apologise to anyone inconvenienced. Please check back later."
A Ministry of Defence spokesperson said: "The Afghan Relocations and Assistance Policy scheme remains open and we will continue to support those who are eligible for relocation.
"We are aware of a technical issue with the ARAP website which we are working urgently to resolve. We apologise to anyone affected."
Former British Army officer Charlie Herbert and local councillor Carolyn Webster are among those who tweeted Defence Secretary Ben Wallace asking for more details about the technical issues.
Ms Webster also asked where "volunteers assisting our military allies left behind" in Afghanistan could "direct those begging for help to save their lives".
Watch: Data breaches blamed on lack of training.
Earlier this month, Mr Wallace was told to "get his house in order" after a third data breach involving Afghans left behind following the UK's evacuation of Kabul.
According to the Defence Secretary, more than 7,000 Afghan nationals have been relocated to the UK.
He added that there are fewer than 200 remaining in Afghanistan as the UK continues "to work with urgency to relocate all those who remain via a range of routes".