Up until today I had text files set to open with Notepad++.
Today I moved my Notepad++ installation, and after that I am no longer to use "open with" to get a text file open in Notepad++, even though the program still works fine and I can load a text file by manually launching the program and then doing a File > Open.
If I go to Tools > Folder Options > File Types > Advanced, then I can manually type in the exact path to the executable that I want to use for opening txt files. However, if I enter the path to Notepad++ and click ok, after closing the window, if I re-open it the field has been automatically restored to reflect the path to standard Windows notepad.
Any ideas? Never seen anything like this in 10+ years of using XP... :-(