I too am having this problem. There are also several folks on other forums posting (today) the same issue. I am running on Windows 7 using compatibility mode and have been using X-CTU successfully for many months. I suspect it’s a windows update that is causing the problem. No proof yet. I will post back if I find a solution.
I was able to get my chip to “un-brick” by unplugging it from my XBee explorer (sparkfun) and plugging it back in. I can now write and configure any AT function set, but cannot set PAN ID or any “AT” settings in any API function set. (Yes I have the “Enable API” selections properly configured)
I found that switching up the function set occasionally got me past some communications issues. (i.e. update to Router AT, then Coordinator API) This isn’t working here.
I’m stuck with the following message now: Lost communication with modem
Time out reading AT command. Stopping read parameters.
Read parameters…Failed.
I think it’s about time for Digi to release an update to X-CTU. Version 5.1.4.1 was released in 2008! Jokers…