several times I have experienced the following problem: When I type in an expression to define a variable and later want to use that variable again I get several error messages saying that the variable does not contain data of the correct type, e.g. I define a list and when I later use it in a function that requires a list as an argument, Mathematica says that it's *not* a list.
After some experimentation I figured out that I had typed in everything correctly. I made the interesting discovery that at the end of the line of the definition of the critical variables, a hidden, white space character appeared. It seems to make a definition invalid. It is also impossible to remove it from the end of the line: When I delete it and hit [Shift]-[Enter], it reappears.
At this point I cannot repoduce the entire situation, but I have attached a Mathematica Notebook which consists of only one single cell, containing this "strange character".
I use Mathematica 8 on a MacBook Pro with OS X Lion.
Attachment: StrangeChar.nb, URL: ,