I've used the original without problems for quite some time. I upgraded to the pro version which has a lot more features but never could get it to work. It would always crash or show errors when I loaded the T/S parameters. Fits of rage and nearly throwing my laptop under a moving bus. Andrew Vaserfirer from HTS figured out the solution. After doing it exactly how he told me it works perfect! I wanted to pass along the info since I know several people have had issues. Again, this is all compliments of Andrew. Ensure that 'Auto calculate unknowns' is on even if you have all the data. This is recommended because WinISD Pro can be very picky about the data and if it is even 1/1000th off it will reject the data so it is just easier to let it do the work. You might notice some small differences in the values from the calculated and the provided, but very rarely are these large enough to substantially effect modeling. This is the recommended method for entering driver parameters [if at any point you need to change the unit of a parameter simply click on the displayed unit and it will change]: Enter Mms and Cms which results in Fs being calculated. If Mmm and Cms are not known enter Fs. If Fs and Mmm or Cms are known enter Fs and the other known value. Enter Sd, Bl and Re. This will result in more auto calculations being made, but Qms and Qts will be blank. If Re is not available, go ahead and enter Sd and Bl. Enter either Qms or Rms, whichever is available, generally Qms is available. If Mms and/or Cms were not provided for input, now input Qes. This will cause some other fields to auto calculate. Enter Hc, Hg and Pe if available. These are not required, however Pe (RMS Power Rating) will give a good idea of how much power signal input to model with. Enter the number of voice coils. NOTE: Drivers using dual voice coils may cause the Bl and Re parameters to change when changing the connection wiring from parallel to series. Be sure to monitor these when changing the connection option, but WinISD should automatically change these values properly. Correct Znom (nominal impedance) if needed. Many times this will change to 6 and should be 2 or 4... or the ultimate resistance (in ohms) you intend to run based on the voice coil configuration and your connection setting (parallel or series). Enter Xmax and any other missing parameters if known and continue. DO NOT change any of the blue auto calculations. If they are only slightly different, this is okay. If they are off significantly, contact the manufacturer or vendor of the driver. If you want you can also tab over to the dimensions page and enter 'Dimensions'. Don't worry about the 'Advanced parameters' tab. The steps outlined should cause parameters to be calculated such that they can be saved without error. If there are problems saving then too many parameters were entered that are likely very close to the calculated value, but WinISD wants the mathematical ideal. Just delete one of the problem values it shows up and try to save after it has been calculated and keep trying until it works. In my experience only Fs needs to be calculated to continue. Read more: WinISD Pro Tutorial and Download (A detailed guide on how to use WinISD Pro) - Home Theater Forum and Systems - HomeTheaterShack.com