Sorry for typo (now corrected) but the problem is shown in the error message itself
'C:\Rlib\Data\1' is not recognized as an internal or external command,
operable program or batch file
The fread function is assuming the filename is "1" due to the space following.
I think there must be a hidden character problem of some sort.
When I use the new functionality in R to select the file by hitting tab within "" makrs it works again.
A puzzle!