If ipsendwin stops at a wpcap.dll was not found error, check the packet-capture installation before reinstalling the application. The DLL belongs to the WinPcap-compatible capture library; installing Wireshark does not, by itself, prove that an older application can load it.
Start with Npcap’s WinPcap compatibility setting. The procedure below follows the Npcap documentation; it is not a new end-to-end test of ipsendwin. The original Japanese post described a Win10Pcap workaround, but adding another capture driver is not a useful first step when the existing installation has not been checked.
Check Npcap before adding another driver
- Close ipsendwin and Wireshark. Save any capture you need to keep.
- In Windows 11, open Settings → Apps → Installed apps. Note whether Npcap, WinPcap or Win10Pcap is installed, including the version.
- Use the official Npcap installer, or the Npcap installation offered by the official Wireshark installer. Installing a capture driver requires administrator privileges and can briefly interrupt networking, so avoid doing it through your only remote connection.
- If the installer offers Install Npcap in WinPcap API-compatible Mode, leave it enabled. This mode replaces an existing WinPcap installation rather than keeping both implementations side by side.
- Complete the installation and restart Windows if requested. Open ipsendwin again and check whether the missing-DLL message has gone.
Npcap has enabled compatibility mode by default since version 0.9985. An already-selected checkbox is therefore not evidence that this was the cause. If the error remains, move on to the checks below. Npcap installation options
Do not download a loose wpcap.dll from a DLL download site or copy one from an unrelated PC. Repairing the official package keeps the library and driver installation together.
Check application startup and packet capture separately
There are two useful checkpoints here. First, can ipsendwin start? Second, can a capture application actually access a network interface? Getting past the DLL error answers only the first question.
| What you see | What to check next |
|---|---|
| ipsendwin still reports a missing DLL | Record the exact DLL name and the installed capture packages. Check the Npcap installation log and any quarantine report; do not disable security software to force the program to load. |
| ipsendwin opens, but Wireshark cannot capture | Check the Npcap installation, capture permissions and selected network interface. This is no longer just an application-startup problem. |
| Wireshark captures, but ipsendwin still fails | Keep the exact ipsendwin error and version. A working Wireshark capture does not establish compatibility with every older application. |
Opening a saved .pcap file is not a live-capture test. Wireshark can read saved captures without Npcap, as its Windows installation guide explains. Use an interface on a device and network you are authorized to inspect.
For installation failures, Npcap keeps install.log in its installation directory, normally C:\Program Files\Npcap. Keep the version numbers and exact error together; they are more useful than repeatedly installing different drivers. Review logs for private details before sharing them. Npcap troubleshooting and logs
