Using 
setcelldata(row,Col,"Data")

For WebTable object, you can retreive the cell data but 
can't set any value directly.

To retreive data.
val = Browser().Page().WebTable().GetCellData(row,column)

To set the value.
If you want to set any value on cell, you can do it on its 
child objects.
So make sure what is the child object of that cell i.e. 
either WebEdit or WebCheckBox or WebRadioButton etc...

Using the method, you can set the value to that child objet.

Using ChildItem method, you can fetch the child object of 
the cell.
Browser().Page().WebTable().ChildItem
(row,col,ChildObjClassname,index of the child 
object).Set "abcd"

or 

Set ChildObj = Browser().Page().WebTable().ChildItem
(row,col,ChildObjClassname,index of the child object)
ChildObj.Set "abcd"

E.g.
Set ChildObj = Browser("ab").Page("cd").WebTable
("de").ChildItem(row,col,WebEdit,0)
ChildObj.Set "abcd"

If the cell has more than multiple similar child objects, 
then you need to take care of the object index.