Whenever I copy text from within Photoshop, I can only paste it onto a second text layer or into a layer's name. The text, however, cannot be pasted anywhere else, such as in a text document or another Adobe program. It's like Photoshop stores copied text inside an internal clipboard rather than using the Windows clipboard. Is this normal?
I guess you should set option Export clipboard = ON in the general preferences. If it's unchecked the clipboard content copied in Photoshop cannot be pasted outside Photoshop.
The other possibility is that your external application doesn't support the copied object format. Copy with the text writing tool the text content and paste into Windows Notepad - it at least supports plain non-formatted text.