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Unable to install npcap on win 7


Hello. I am using W7 X64 with SP1, and have the driver installation issue as in this question. If I try installing with the command line, I have that message:

c:\Program Files\Npcap>NPFInstall.exe -i
Npcap LWF driver has failed the installation.

I tried to install the W7 update posted by Pascal Quantin, but Windows tells me it's already installed.

Any clues?

Best regards,


asked 27 Jan '16, 02:28

NelsonB's gravatar image

accept rate: 0%

converted to question 27 Jan '16, 03:09

grahamb's gravatar image

grahamb ♦

Please don't create a new question as an "answer" to an existing one, this is a Q&A site not a forum. Please see the FAQ for more information.

(27 Jan '16, 03:09) grahamb ♦

One Answer:



For Vista x64 and Win7 x64 users:

If you still get the pop-up window that said Windows requires a digitally signed driver (or get error 577 when executing net start npf), please try these steps:

1) Install Microsoft's KB3033929 patch successfully (it should requires reboot).

2) Install latest Npcap 0.05-r8.

3) If step 2) still fails running the driver, then reinstall an alternate version of Npcap you NEVER installed on the machine before (like 0.05-r7, if you unfortunately tried 0.05-r7 before step1), then try 0.05-r6.) to "flush" the driver cache. You should use the same option of Install Npcap in WinPcap API-compatible Mode as you did in step 2). This installation of 0.05-r7 should work.

4) Reinstall back the latest Npcap 0.05-r8. This second-time installation should succeed.



You should install the lastest Npcap 0.05 R14, all signing issues should have gone.

answered 29 Jan '16, 09:56

Yang%20Luo's gravatar image

Yang Luo
accept rate: 4%

edited 26 Feb '16, 19:10

Hi Yang, I appreciate your efforts on this driver and the given support. I followed all your steps, it still not working.

(02 Feb '16, 07:03) NelsonB

You probably have the experience of installing 0.05-r7 before following these steps, right? The "alternate version" of 3) should be a Npcap version you never installed before, maybe 0.05-r6 or 0.05-r5 (one that you didn't install on that machine)

(02 Feb '16, 07:25) Yang Luo

My first experience with the Npcap driver was with r5. Then I tried with r8. Following your comments, I installed r7 then r8 again. Is there any possibilities to use the signing method used on the winpcap npf driver? I never went through a driver signing process, so I cannot give more help than test your package and give you feedback on it.

(03 Feb '16, 01:28) NelsonB

OK. Then currently, I think the most workable solution for you would be disable the driver signing enforcement for your system. This is absolutely usable I think.

(03 Feb '16, 06:51) Yang Luo