Polygon to Raster Error 999999

[Dana1]

Hi! I'm working in Arc 3.1.3, and I'm running a code that has worked for me up until this week. Suddenly it's started throwing a Error 999999 on my Raster To Polygon call. I have the section of code that I'm running below - I'm taking a buffer of an input polygon, and converting that buffer to a raster to I can use it to create a DEM with a burned-in stream for an area. 

[DanPatterson]

If the output location is a folder, try addint a 'tif' file extension