Use "raster combine", error 010158, 010067, how to solve them?

[ShuranZhou]

Hi, I'm combining two file system rasters using raster combine, obviously it turns out that they couldn't be successfully combined becuase of error 010158--unable to open file, and 010067--error in executing grid expression..I can open the files under table of contents, and for the second error i'm not sure what it is?? I read the help info on the errors but I couldnt figure out how exactly I could solve them? Anybody have any ideas?

Thanks!!

[JeffreySwain]

File System rasters, would that be Esri GRIDs?  If so can you indicate if the path has spaces or special characters in them?  Or if you maintain the same location, but change the format of the rasters to a .tif or .img with the Copy Raster tool, will the process work. My assumption is that the tool fails due to the path of your data.