Remove that check and set manually the value (48000) make sure you have enough space!
ahhhhh ok but this is normal! FREE is something different from AVAILABLE but actually you must check the AVAILABLE and not the FREE ). You still have more than 10 gb )
Basically the difference between FREE and AVAILABLE is:
FREE: it contains 0 (zeros) and actually has never been used (this will always be a small number, some exceptions may apply...)
AVAILABLE: this memory has something inside but... it's not required. Some (too many) programs use the RAM and then they forget or don't want to free up the memory completely. So this part of ram is in stand-by. actually is not free (because it has something inside, not used but it's still something), BUT windows or other programs can use it to work )
Don't watch the free memory, better the available )