The error message typically occurs when using an outdated version of Wireshark or TShark to open a packet capture that uses the LINKTYPE_LINUX_SLL2 format .
The error "-pcap network type 276 unknown or unsupported-" is not a bug but a telling you that your tool doesn't speak the file's link-layer language. Whether the source is a Nordic BLE sniffer or a corrupted header, the solutions range from trivial (upgrading Wireshark) to surgical (hex editing the pcap header).
I believe type 276 is a specialized header (possibly related to [Infiniband/Raw IP/proprietary link]), but I can't find documentation on how to force Wireshark to interpret it.
Before you fix the error, confirm exactly what is inside your file.
You are using an older version of Wireshark or tcpdump that predates the addition of the SCLP link type.
library is up to date, as this library provides the foundational definitions for link types like 276. Re-encode PCAP Use a tool like (bundled with Wireshark) or TraceWrangler