I don't believe I ever sold an A2100 machine with less than 4MB of program storage so the amount of memory you are referencing sounds extremely small. The hard drive size does not directly apply to the amount of program storage the control has because additional program storage was sold as a control options (keep in mind this control was sold when Fanuc was still quoting memory in terms of "feet of tape" at extremely high prices rather than Megabytes or Gigabytes that Cincinnati was). Perhaps your options are not configured properly to allow access to the additional program storage that was likely purchased with it.
I believe Siemens will still sell options for larger program storage if you are interested, but even if you have limited program storage, you can still save the file on the control's hard drive (or network drive) and when registering the program use the "Register External" function. This links the program to the external file rather than taking up the program storage.