tcpdump on LTM

when I try to save it to a file type and export it off the LTM and try to open it in wireshark for analysis, I get the following error. "The file "test.pcap" isnt a capture file in a format Wireshark understands."

what the tcpdump command did you use? was it -w option?

-w   Write  the raw packets to file rather than parsing and printing them out.  They can later be printed with the -r option.  Standard output is used if file is ââ-ââ.  When writing packets in this manner, the first packet in the file will be a pseudo  packet  indicating  the  command line  used  to  run  tcpdump and some system information.  This pseudo packet is not counted in the packets captured summary information nor when limiting the length of the capture with the -c option.