By default, SMS will not install a package onto a distribution server that has less than 100 MB free disk space. You can override this default by changing the SMS Drive Minimum Free Space in MBytes entry in the Site Server registry. You might want to override this default if the drives on your distribution servers are not particularly large. By changing the registry value from 100 MB to something like 10 MB, your distribution servers could store more packages.
To change the free space requirement
Open the registry to the following key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SMS\Components\SMS_Despooler
Select the SMS Drive Minimum Free Space in Mbytes value entry. Specify the desired minimum value for free disk space on the distribution server SMS drive. The default is 100 MB (specified in hexadecimal as 0x64).