Load the zip file in a hex editor. The first 2 bytes should be 50 4B (that's PK), and the first filename should start at byte 30 (1E hex). Change the filename there to legal characters. e.g. between 41 and 5B (that should be all caps)... watch for the 2E, since that's the dot before the extension.
It sounds to me like the whole file is corrupted though, not just the filename of the compressed

Thanks for the additional info - I did check the file, the first two bytes are as advertised. Problem occurred in the file when I was zipping it using AbaleZip code - accidentally had a global variable set to null and that set the file name to a null in the file. Not sure wether I would have to "insert" a file name at that point - do you know what the header structure is for a zip file?

In extreme cases for corrupted zip file recovery software try ZIP Recovery Toolbox on it. If it's corrupted ZIP Recovery Toolbox has the best repair routines of all the zip utilities... it will make a file named ***.zip, then you should be able to extract whatever is in it from that container. There is a full demo version and thus you can check the software efficiency. [ Register or Signin to view external links. ]

Looks like you'll need to alter byte 27 (0x1B) to something other than 00 to specify the size of a filename (e.g. make byte 27 say 0A if you want to insert the filename fooman.txt starting at byte 31)... so the edited file should 'grow' by however many characters the filename.ext adds.
From [ Register or Signin to view external links. ]

You've been very kind in your efforts to help. Thanks for that.