I've been getting the attached error for say about one week now.  I'm running Windows 10 Pro 64, using 64-bit UltraEdit v27.00.0.30.

Once I open two instances or more of UE, this error will slowly pop up, I'd say every 10 minutes or so one would pop up.
It's part of UltraEdit as when I hover my mouse over the UE shortcut on the task bar I can see all these error windows along with the opened UE windows.

Have anyone encountered this?
It's getting quite annoying.

I want to add that, the two (or more) instances of UE are not editing the same files. They would have temp files though, those that are named Edit1, Edit2, etc. that are unsaved.

I get the same error since upgrading to x64 v27.00 (v26.20 was fine) and have three instances of UltraEdit open for different projects. I only get two popups though, and they always start only after resuming my PC from sleep. If I close two of the UltraEdit instances, the errors go away and after restarting them the errors do not re-appear until waking up the PC from sleep again. All files open in all three instances are local to the PC with no crossover between instances. I've already 'fixed' the errors by restarting UltraEdit today, but when it happens again tomorrow I'll have a session with Process Monitor to see if it can identify the cause.

Hmmm... I thought this would be fixed in the latest version. When I had this problem, support worked with me and gave me a hotfix - I don't remember the exact version number. But I've updated it once after this hotfix so I'm thinking they have put the fix in the latest version. The version I have now is 27.00.0.72.
Is this what you use?

Thanks for the update. I've installed the update and will see tomorrow if it fixes the issue for me. Here is what ProcMon said was the cause:

High Resolution Date & Time:    09/07/20 08:10:56.5995713
Event Class:    File System
Operation:    CreateFile
Result:    SHARING VIOLATION
Path:    C:\Users\<username>\AppData\Roaming\IDMComp\UltraEdit\volatile\ue.vod
TID:    9396
Duration:    0.0000329
Desired Access:    Generic Read
Disposition:    Open
Options:    Synchronous IO Non-Alert, Non-Directory File
Attributes:    N
ShareMode:    Read
AllocationSize:    n/a


High Resolution Date & Time:    09/07/20 08:10:56.6643934
Event Class:    File System
Operation:    CreateFile
Result:    SHARING VIOLATION
Path:    C:\Users\<username>\AppData\Roaming\IDMComp\UltraEdit\volatile\ue.vod
TID:    10396
Duration:    0.0000224
Desired Access:    Generic Read
Disposition:    Open
Options:    Synchronous IO Non-Alert, Non-Directory File
Attributes:    N
ShareMode:    Read
AllocationSize:    n/a