I am still having this problem but the DWP Future Pension Centre say there is a problem with m y account or NI no (not sure which) and so far this seems the only explanation for why I cannot access my State Pension Forecast (and until it is fixed they will not send me a forecast either!); it is not a problem with my Government Gateway ID which is fine and allowed me into my Personal Tax Account without any problem.
HMRC (once I could get through to them) confirmed that my details were all correct and gave me a precise figure for what the shortfall in my NI contributions was. It is however nigh on impossible to get through the HMRC voice menu to speak to an actual person but the DWP phone does get answered pretty promptly and they are as helpful (I think) as they can be and they may be able to say if they think there is a problem with your account.
Not sure if this is the right place to raise this but I have been trying for days to access the service for checking one's pension forecast so I can see if I need to make any NI contributions, and it persistently tells me this:
"Sorry, there is a problem with the service
This might be caused by a high number of people trying to use this service at the moment. Try again later."
Can anyone help?