*E,TRFILEIO: file I/O Error using textio.all library in Sigasi

I'm trying to use the std.textio.all library but I'm getting the following error:  

ncelab: *E,TRFILEIO: file I/O error.
cannot open 'uart_rx_inputs.txt' for reading

The input file, uart_rx_inputs.txt, is pretty simple:

 1.100024 sec
 35
 1.109606 sec
 03

So, I really don't know what to troubleshoot.  The testbench file and this input file are both in the same directory.  I cannot find any clues to the problem by perusing forums.  Any ideas?  Please help!

~ melisanthi