What prevents export of a private key from Mavericks keychain? In Mac OS X Mavericks, I'm not able to export a private key from keychain. I'm getting the following error message:
 /* In dark wake, no UI possible */

Searching it in Apple documentation fetched the following details:

value: -25320

Description: The user interface could not be displayed because the system is in a dark wake state. Available in OS X v10.7 and later.

Can someone please suggest a solution or the cause of problem?
It appears that your system was mistaken about being asleep (because an internal flag it used to keep track of sleep state got out of sync with the true state). As you confirmed later, a reboot fixes this problem.