Illegal characters in path. ?

I've got an error:  "Illegal characters in path." But i don't understand why ?

The code is:
png = ConfigurationManager.AppSettings["localpath"] + "images\actie.png";
imgF = System.Drawing.Image.FromFile(@png);
In my Web.config i have:

 <add key="localPath" value="C:\websites\HV tweewielers\" />

The error is on the last row, if u get with the arrow on @png i get: C:\\websites\\HV tweewielers\\images\actie.png
But the path is correct ... Quite strange because it works perfect if i add: c:\websites\hv tweewielers\images\actie.png ....
...