I am not familiar with the Marshal method you are using to allocate and fill the capability. But it looks to me that you are not allocating enough memory.
There is an example in the spec in section 2-19 for STR32 that should be easy to change to STR255.
Marshal.WriteInt32(pv, 2, Convert.ToInt32(value));
If Value is a STR255 then you probably want to use a method similar to
Marshal.WriteString(pv, 255, value);
You might also want to do a MSG_GET on CAP_PRINTERSTRING and see what is supported. There might be some predefined strings in the enumeration.
Regards,
Jim Watters
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