Hmm i never got the io error myself. Can the .tga file be found?
Also if you know the filename/path used is correct can you give a linenumber also as the code you mentioned is used in several parts in the tga loader.
The tga loader is a bit of a quick hack.
Yeah.. The TGA can be found. The error happens on the following line:

[pascal]
// check, if we have a valid pointer
if (filename='') then
begin
result := false;
exit;
end;

// open filename in "read binary" mode
AssignFile(lfile, filename);
Reset( lfile,1 ); //Read bytes

// seek through the tga header, up to the type:
BlockRead(lfile,buf,1); << ERROR HERE
BlockRead(lfile,buf,1);
[/pascal]

I don't know why i get this error, because I have little experience with files. I always use filestreams.