help i m getting internal error...how can i resolve it

Internal Error: Sub-system: ASM, File: /quartus/comp/asm/asm_bit_connect.cpp, Line: 550

!has_been_used

Stack Trace:

0x1e73d3: asm_assemble + 0xa9c (comp_asm)

0x1e6d97: asm_assemble + 0x460 (comp_asm)

0xd4e8: qexe_get_command_line + 0x7a8 (comp_qexe)

0xfd58: qexe_process_cmdline_arguments + 0x3f8 (comp_qexe)

0x25056: GEN_PROFILE_BINS::initialize + 0x216 (CCL_GEN)

0xfdee: qexe_standard_main + 0x4e (comp_qexe)

End-trace

Quartus II Version 9.1 Build 350 03/24/2010 SJ Web Edition

Service Pack Installed: 2