off grid error skill
When GDSII or appropriate layout file is sent for Fab, Mask is created from the GDSII. Mask is prepared by putting "black dotes" on a special glass. If the grid is not clear, then the tool which puts those dotes cannot work. (Simply put).
So you Have to Move the Layout to one of the dotes in the Virtuoso Layout Editor.
The problem while "re-gridding" is that the dotes may not be in their minimum value specified in the TechFile. So, goto OPTIONS --> DISPLAY . In the "Minor Spacing", put the minimum vlaue, say 0.05 for 0.35um or 0.005 for 0.18um tech. Then check the locations where you have off-grid error, move it to the right location.
To vbhupendra: You have to move it. There is no other way. I think I had a SKILL script for automatically moving the whole layout to 'Grid'. If I find it, I will post it.
Srivats
P.S.: It is very irritating to look hundreds of grid-errors. You can use an avSwitch option in Assura DRC deck so that you can "switch it OFF" (Assura DRC GUI has Switches TAB) and look at them after you have cleared other errors.
However, it is recommended to clean them at first DRC error run itself.