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Two existing EXEs, one written in C++ and Windows SDK, one written in C# and .NET 4.5.1, suddenly cannot open COM ports, "access denied". HyperTrm.exe has no problem opening the same ports that both EXE cannot open. Some recent update for Windows 10 has caused this problem. What is necessary to regain access to the COM ports?
Are there any issues with the COM ports when view in Device Manager?
Access Denied typically happens when some other application is using the port. Is Hyperterminal running in the background? Have you rebooted the system and ran these applications?
Sean, trying to post a reply, hit "Submit" and nothing happens, no error, no post.
See attached.49674-com-problem.txt
Hello @Frank Natoli , could you try this official sample to see if it can open the COM port successfully? Run it as normal user not as administrator. You can share your content of the com-problem file in your question body or in multiple comments if it is too long to post in one comment.
I went looking for a HyperTerminal like solution I developed that performed COM port communication. I cannot seem to locate it. I would recommend trying a different serial port application as RitaHan suggest just to see if there is something your applications that are causing an issue.
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Every online discussion of COM port Access Denied errors says the same thing - make sure the COM port is not in use by another program. Does Windows have a BUILT-IN way to "make sure" or do I have to look for a 3rd party tool?
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Make sure that the port is not already open by another program that uses TAPI, such as a Fax program. Hyperterminal is TAPI-compliant, so it can use grab the port away from the other TAPI program. This would explain why Hyperterminal has no problem opening the port while your own program fails with "access denied".
Well, you can use netstat -an to see if the port appears in the list of ports in use.
Netstat has additional options that you can see by means of "netstat -?". If I remember correctly, one of these options lists which is the program that is using the port.
Netstat only shows network ports, not serial (COM) ports. Please correct me if I'm wrong.
I used Portmon for Windows v3.03 several years ago and it works on Win 10. I have also used Free Serial Port Monitor. There are other serial port monitors that you can find with a Google search.
You are absolutely right. This question is quite old, and I had forgotten what it was about. I mistook it for other more recent question that had been asked in a different forum, where the problem was precisely network ports. Next time I reply I´ll be more careful to check what exactly I am responding to, rather than assume that it was the last thread I had been following. Thank you for the correction.
I love how this one careless answer has managed to poison every AI data set that has information regarding this issue.