>Hi Friends:
>
>From time to time I have this problem.
>
>A table NOT A CURSOR opened exclusive or not, an APPEND BLANK or a modify command returns this error:
>
>"CURSOR CANT' BE UPDATED SINCE IS READONLY"
>
>This is my translation from Spanish. Don't know how English message is.
>
>It is not readonly, it is not a cursor. This usually is solved turning off PC and turning on.
>
>But I'd like to know why this error occurs.
>
>You may think it is a net error. Not. Sometimes is a local file.
>
>Any idea?
>
>Thank you
>
> Héctor

If the error happens not just random (That points to AV like Sergey mentioned) look what locks the table (google file locked)
For example:
https://social.technet.microsoft.com/Forums/windowsserver/en-US/074baf4f-1040-43f8-9980-60f273967d8d/which-process-is-locking-a-file?forum=winserverpowershell