DXF problem on AutoCAD LT 2014/AutoCAD 2014

[ggrotto]

Goodmorning forum
I'm writing for a strange problem.
Using different types of AutoCAD LT (2012-2014)and with different workstations (HP z230 xeon- HP z4220 xeon - EliteBook8760w i7) with different operating system (w7 pro - w8.1 pro) happen this:
If i draw a dwg file, I save it,Then I choose save as DXF ( I choosed different version: 2000-2004-2007-2012-2014).I close my AutoCAD LT or AutoCAD application and I do a double click on DXF files.
An advertise appeared and say this: C:\user\...\document\draw1.dxf is allready used or only read mode. Do you want to open the file in only read mode?
If i choose "NO", I can work with my file, save it on himself , modify ecc ecc...
The strange things is this, when AutoCAD/ AutoCAD LT is running and I open the file from File --> open, all works fine without the advertise. The same file have no problem.
I think there isn't a problem on the file. I say this because I had check in the option( of DXF file) and there isn't flag in only read mode, and I made a lot of DXF starting from old and new files but the result is the same (only if AutoCAD application isn't running).
A similar problem appeared on my EliteBook 8760w whit W8.1 PRO, not with ACAD LT but with ACAD 2014 and during the opening of DWG and not DXF.

Anyone have a solution for this? is a know problem?

I've seen that in AutoCAD LT 2009 and in Autocad architecture 2012 all works fine without problem!

[pendean]

What is Windows Explorer set to use with DXF files: you're not describing an AutoCAD issue from what I can tell.

[ggrotto]

Hi Dean,
what kind of setting are you speaking about? there is something to check on windows? for DXF files the default program to use is AutoCAD LT application as you can see in the pictures.

I'll make a screen video to show the problem.
I'm Italian so the error will be in italian language =(