It sounds like your error message is saying that somewhere else in the render queue you're rendering the exact same frame. The "you're going to overwrite a file" dialog is not the same as the one you're talking about.
Oh, I see what you're saying. That's irritating.
Try it in CC 2014 (it's often faster to render in CC 2014 anyway since it has multiprocessing - assuming your comp can benefit from multiprocessing).
You have two renders cued up at the same time. Uncheck one of the renders, render that, then check the second render and render that. The error message makes sense to me because the renderer does not know what the first file name is until it starts rendering. That should give you a work around.
And what if i have some 65 renders in a queue?
Image sequence : Use Comp Frame Numbers
BTW, I cannot reproduce your error message in the CC 2015 build 22.214.171.124 IOS 10.10.4. It is working for me just as it always has.
my version is also 126.96.36.199, and OSX 10.10.4
Does it mean, there is some option to check, in preferences or somewhere?
I can't tell. There are no options that I know of that would cause this problem. Are you using dynamic link or running the AME in the background. Try rebooting, open only AE, create a solid or a shape layer in a new comp and animate it over a few frames then try adding the comp to the render cue and set up the output module to render an image sequence and the render settings to render the entire comp, duplicate the item in the render cue or add it again and pick a different range and then render and see what happens. If it works without problems then open up the project that is giving you problems and start digging into your settings.
No. It's not a problem of the exact project. This is the problem on every project, new or saved one, on every machine, with Afx CC2015.
Steps, to get this "effect" :
1. Open After Effects
2. Cmd + N (creates new comp. Set composition length to more than 1 frame)
3. Cmd + Y (Adds new layer)
4. Cmd + Ctrl + M (adds render to queue)
5. Cmd + Ctrl + M (adds another render to queue)
6. Open Render Queue Tab
7. Select both renders and choose Output module to Image Sequence (make sure the checkbox Use Comp Frame number is checked in)
8. Click on Render settings to first render in Queue. Choose Time Span Custom and set from 1 to 2
9. Click on Render settings to second render in Queue. Choose Time Span Custom and set from 8 to 9 (it's no matter what exact numbers you choose, reason is to take different numbers of the sequence)
10. Click on Output to the first render in queue (File name, UnClick box "Save in Subfolder" and choose name "Comp1_###"
11. Click on Output to second render in queue (File name, UnClick box "Save in Subfolder" and choose name "Comp1_###"
You're done. You've got this error (or not error, just notification dialog, call it what you like. But You can't set up 2 renders, or even more with the same filenames, even this are sequences with different numbers)
If really not.... Please let me know, what should i change in settings, in prefs, in wherever
If you have 65 renders in cue then I'd write a script that renders a comp then adds a new comp to the cue and renders that or set up multi machine rendering. It's the only way I know of to avoid the error message you are getting. The point I am trying to make is that this works as it always has. When I render a replacement section I usually just add the comp to the render cue, pick the folder and accept the overwrite file option. I know of no setting where you can override the warning force the render cue to use the same path and file name.