INDD File Opens Read-only / ZIP Files Suddenly Open In BG

One of my co-workers has been having this odd problem and I'm not sure what to make of it. On occasion, she goes to open an INDD (Adobe InDesign) file which is stored on our Windows 2003 server, and it opens as "read-only." She opens the file to make changes and can't because InDesign won't let her save any changes to the file.There's no apparent reason for this - she has full access to the file, the file's read-only bit has not been set, and there's plenty of space on the server.What she usually does to get around it is to "Save As." over the file she's just opened. That normally works. On occasion this doesn't work and she has to "Save As." to her desktop, then "Save As." back over the original. It's a pain for her at the very least.

What's odd is that I've checked the "open files" list on that Windows 2003 server when she gets the error. Her workstation suddenly opens a whole handful of zip files located on the same Windows 2003 server (some of our digital artwork comes in zip packages). They are opened in read mode only (READ, not READ-WRITE).When she does her "save as." and gets past the error, the read locks/handles on the zip files are closed also. The ZIP thing sounded suspicious to me and I scanned her computer (as well as the ZIPs) for viruses. Nothing came up. I have since even re-installed the entire operating system (Windows XP Professional, SP2) and still the same behavior.Now what's funny is it's only InDesign (CS). All of her other apps (even other Adobe apps) seem to behave correctly.

I've even inspected her network wiring and replaced her aged CAT5 with brand-new CAT5e, which needed to be done anyway. (we run gigabit). Net connections are solid (she's only 20-30 feet away from my office where all the office switches are located, which makes things easier). No one else in the office has the problem, and her computer (and software installed) is comparable to everyone else's, at least in her department.
Our software is too old to get support from Adobe (upgrading to CS3 isn't financially feasible at the moment but not sure an upgrade would help if I don't know what the problem is), and I've tried the official Adobe forums with no luck. I didn't get very far - most of the people on that forum aren't PC/NET tech experts, just Adobe users (for the most part). It seems that way, anyway.I guess I'm running out of ideas. What should I do to figure out what's going on here?