viVPrintf can't use "&"

hi:

I want to save image from VISA

I use 

status = viVPrintf(vi, "ISKAVE:IMAGE " "FALE1"",JPEG,SCR,ON,INVERT" + vbCrLf, 0) 

it can save image.

but i use 

 Dim filename As String = VI_filename.Text

status = viVPrintf(vi, "ISKAVE:IMAGE " & filename & ",JPEG,SCR,ON,INVERT" + vbCrLf, 0) 

it can't work!

why?