Have been experiencing the same problem for a couple of months now. Nagios will run fine for a few days or even a week or 2 and then suddenly refuse to start.
The only solution until now is to save the full etc folder, remove and reinstall Nagwin, then copy back the etc folder. That always fixes the problem but is not so convenient.
Please assist based on the information below.
When the problem appears I see a nagios.exe.stackdump file appear which has the following contents:
Exception: STATUS_ACCESS_VIOLATION at eip=6111354A
eax=7F736F6F ebx=00000000 ecx=2F736F69 edx=74706F2F esi=010F02C8 edi=010F02B4
ebp=1991A288 esp=1991A284 program=C:\Program Files (x86)\ICW\bin\nagios.exe, pid 8300, thread unknown (0x1FC8)
cs=0023 ds=002B es=002B fs=0053 gs=002B ss=002B
Frame Function Args
1991A288 6111354A (74706F2F, 2F736F69, 74B011D8, 000000E0)
1991A318 61111FA4 (010F02B0, 00000007, 00000004, 0042B040)
1991CD58 0042B7FC (00000000, 00000000, 00000000, 00000000)
1991CD98 610E7455 (0112E220, 1991CDD4, 610E73A0, 0112E220)
End of stack trace