Generally speaking:
1) Only name GIS datasets using letters, numbers, or an "_".
2) Always start the name (database names, rasters, featureclasses, field names too!, etc.) with a letter (not a number or an underscore).
3) Avoid spaces and special characters (such as a ".", "&", "#", etc.).
4) If you can help it, keep names <= 10 characters. There are many exceptions of course, but...
I have followed these four basic rules for 12 years, and have never gone wrong. Sorry, but I think you will have to rename your shapefile to get this to work (maybe reformat to a FGDB, and the "." may be supported in that format?).