Why does the FIR Compiler appear to hang when the Synchronous Clear (SCLR) option is not selected and targeting a Virtex-II/-II Pro or Spartan-3/-A/-AN device?
This issue is fixed in the FIR Compiler v3.1.
Not selecting the SCLR is not allowed for the Spartan-3 non-DSP family parts; the core must have a RESET pin. Unfortunately, the GUI in the FIR Compiler v3.0 does not restrict you from making this selection, which can cause the netlister to hang and not finish. Consequently, you must make sure that the SCLR control option is selected.
See (Xilinx Answer 29138) for a detailed list of LogiCORE FIR Compiler Release Notes and Known Issues.