Slic3r version .071 error

I am using Slic3r 0.71 precomplied for Windows on Windows 7. Slic3r 0.71 has been work great for me until today. Today I keep on getting the same error no matter what I try to slice and with what configurations. I keep on getting the same exact error : Argument "" isn't numeric in numeric ne (!=) at C:/Users/peter/Desktop/Slic3r/lib/std/Slic3r/Print.pm line 634. Any help at all is much appreciated.

I'm also getting this error on both my pc and Mac.

I got that error (albeit in a different version) . After lots of searching around I realised that I'd changed my settings and replaced a zero in one with a blank

I got similar error.

Argument "\x35\x30..." isn't numeric in multiplication (*) at Slic3r\lib\std\Slic3r\GCode.pm line 387.

I found out that it was caused by value "20mm/s" written in the "Modifiers: First layer speed" field in "Advanced" tab.
I changed it to "50%" and the error was gone.
I think it is a bug and should be fixed. Mainly because the text says that there can be "mm/s or %"