IsolatedStorage createFile not working

I am getting FileNotFoundException when I make the following call:

IsolatedStorageFileStream rootFile = store.CreateFile("abc.txt");

However, if I have a textbox on my page and do:

IsolatedStorageFileStream rootFile = store.CreateFile(textBox1.Text)

then this works.

I am using Silverlight 3.

Any ideas why I get the error?

JD

Is the FileNotFoundException internal to the CreateFile call? Check here.