Wireshark provides you with additional information generated out of
the plain packet data or it may need to indicate dissection problems.
Messages generated by Wireshark are usually placed in  parentheses.
C.1. Packet List Messages
These messages might appear in the packet list.
C.1.1. [Malformed Packet]
Malformed packet means that the protocol dissector can't dissect the
contents of the packet any further. There can be various reasons:
Wireshark erroneously has chosen the wrong protocol dissector for
this packet. This will happen e.g. if you are using a protocol
not on its well known TCP or UDP port. You may try Analyze|Decode As
to circumvent this problem.
Packet not reassembled
The packet is longer than a single frame and it is not reassembled,
see Section 7.6, “Packet Reassembling” for further details.
Packet is malformed
The packet is actually wrong (malformed), meaning that a part of the
packet is just not as expected (not following the protocol
Dissector is buggy
The corresponding protocol dissector is simply buggy or still
Any of the above is possible. You'll have to look into the specific
situation to determine the reason.
You could disable the dissector by disabling the
protocol on the Analyze menu and check how Wireshark displays the packet
then. You could (if it's TCP) enable reassembly for TCP and the specific
dissector (if possible) in the Edit|Preferences menu. You could check the
packet contents yourself by reading the packet bytes and comparing it to
the protocol specification. This could reveal a dissector bug. Or you
could find out that the packet is indeed wrong.
C.1.2. [Packet size limited during capture]
The packet size was limited during capture, see "Limit each packet to n
bytes" at the Section 4.5, “The "Capture Options" dialog box”.
While dissecting, the current protocol
dissector was simply running out of packet bytes and had to give up.
There's nothing else you can do now, except to repeat the whole capture
process again with a higher (or no) packet size limitation.