Yes I am able to access the GetROProperty and then get the value of the row number of the last row, the property is "bottomrow" which helps but still many other things like getting the values from a particular cell are still difficult to retrive.
I've had very similar problems with .Net WinForm grids (ours are DevExpress and ComponentOne).
One issue that produced symptoms like you described depends on how you mapped the grid. There are several types of datagrids that all get represented as SwfTable (MS, DevExpres, etc.) and there was a bug in 6.5 (I think) that recorded the wrong kind of grid depending on how you recorded it (via recording vs. Obj Rep learn button). Unfortunately, I can't remember which one produced the problem, so you may want to try to remap the grid both ways and see if that solves any of the problems you're having with the various method calls.
Another side note (probably no need to mention this), but be sure you're calling SetView method before calling anything on the SwfTable.
If this doesn't work, let me know. There were a couple of other issues we encountered that may help, but I'd have to do some digging (it's been several months)