I don't see this behavior with CS5 under OSX 10.7.4.
Are you running 126.96.36.1993? (Hold down Control and select About InDesign)
Have you tried FAQ: How do I reset or "trash" preferences?
I assume your zero point is set to the left margin, i.e. 3p4 relative to the spine?
You haven't mentioned either your desired column width or your gutter size for the 4C grid, so it's a bit tough to be certain of what you wanted. I assume you wanted a 4-column grid with 5p gutters, so your first grid line should be at 11p1 (relative to the left margin)? Because that's what I get.
And the far left and far right guides are right at 0p0 and 59p4.
InDesign internally uses points for its calculations (and floating-point decimal fractions thereof), but your problems sound like round-off errors. Yet they are far too large to be round-off errors...
Have you tried recreating your document from scratch?
On another machine?
As a last resort, you can export to IDML, unzip the file, and look at the actual coordinates of the margins and guides (this will be a pain).
I recall a rounding error bug back around CS4 or CS5, but I don't recall if it affected windows. My memeory is that it incorrectly displayed digits in the thousandths place in the panels, but that the dimensions were actually correct. Are you using points or inches as your ruler units?
And by all means, make sure you patch to 7.0.4 as John suggested.
In my example above, I had in mind a 5 column grid with 1p gutters. So the first column should begin at 11p0.8, the second column at 23p1.6, etc.
Instead, everything is off by .004.
As far as recreating the document, I have not yet tried creating it from scratch (we work from templates), but I will.
I looked through the changelogs for the 7.0.x updates, but didn't see anything that looked like it would bear on this issue. Not sure if I can talk the tech people into upgrading us or not.
Ah, you had said a 4-column grid, but you meant a 5-column grid. Gotcha.
Please try recreating from scratch. It's essentially what you've asked the rest of us to do (and what I did), so you should take the time to do it as well.
7.0.4 (and 7.0.3) fixed innumerable issues, not all of them in the ChangeLog. The benefit is huge, you should push for it. What version are you using, then? 7.0.0? You did not specify.
If I change the guide grid to 5 columns, things are fine.
Oh yes, originally you said:
Because of the way our ad software works, standard columns have to be set at 6 columns with p8 gutters. We make these columns white, so they look invisible on the page.
What do you mean by making the columns white? Do you mean you set the column guide color to be white instead of maroon? Or something else?
So you are using a template made in a previous version that you're opeing directly in CS5? In theory this shoud work, but there are enough reported problems withthis workflow that I HIGHLY recommend you recreate the template, or at the very least export it to .inx from the original version and resave that file as a new template in CS5.