A quiq work around this might work [ at St Regis they actually block room type but at other properties it works ]
When booking Marriott/spg award reservation there usually needs to be a base room. Sometimes though, the base room may be available but not for points and a message will pop up saying "this hotel does not take award reservation at this time" [ clicking >< does not help ]. The solution is to make the reservation on different dates and call the hotel directly [or ask marriot to contact the hotel] and ask them to change the dates.
The name of the system where marriot/spg can change dates is called Fossi [not sure if spelled correctly]. I'm not sure central Marriott can do it but on hotel level they definitely can.
One caveat, this will most likely will only work if there the same room type . If there is same room room then the system will force itself to initiate to a new reservation which will not work because there are no base rooms available.
This is my understanding, if any1 has better work arounds, please post.
I did this for the Residents Inn Surfside on blocked dates and worked like a charm.