4294967296 is 4GB; 4294967295 is usually the limit to the size of what an uint32_t pointer can reference. Change your datatype.

However, consider:
Your object must exceed that value or you have exhausted heap memory or exceeded the process memory limit if one is set. What exact error did you get? Fix your code to display what the error is, i.e.

Code:

   // you need to include <errno.h>
   if( !lbuf1 )
   {
      fprintf(stderr, "Fatal error %s\n", strerror(errno));
     // or use perror
     // perror("Fatal error");
      return( -2 );                // insufficient memory
   }

Did you check:
ulimit -a for the process. What does free show? While the code is running?

There are other factors that can also limit allocating giant chunks of memory - heap fragmentation. I do not know how to report that on RH or CentOS from the command line. I do know you can get heap information by writing C code to look at anonymous memory in /proc system-wide.

Heap framentation can occur when you make a bunch of calls to malloc or realloc in succession where the size continually doubles. And there are other process that tie up substantial heap memory or shared memory. You get to a point where the contiguous size chunk you want is not available but the total free memory (made of lots of smaller chunks) exceeds what you need. java is notorious for that - so much so that one of the startup parms allows you to force java to get max possible heap when it first starts.

Start by finding out the exact error, you are assuming ENOMEM.