>While compiling the project (for simplicity, I just selected a "rebuild project"; all other options are unchecked), I get a message "error reading file". Not knowing which file caused this, I created a new project; the "error reading file" appeared for one particular class library, more specifically, a file called vfxform.vct (part of the Visual Extend framework). According to the help, the error message means that:
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>"The operating system returned an error while Visual FoxPro was attempting to read the specified file."
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>However, I can open the class library, and make a duplicate on disk. What might cause this?
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>I also checked whether the file isn't read-only. (It isn't.)

Any time the OS returns a hard file system error like that, you should run CHKDSK from a command prompt on the volume in question. Also check your System Event Log and any S.M.A.R.T. messages that may have been recorded in the BIOS, in case your hard disk is failing.