Changes you made to the file since you checked it out conflict with other changes made (and checked in) to the source file by another user. This error has the following cause and solution:
Open the file in your working folder and search for six consecutive equal signs (======). VSS uses these to mark the location of a conflict.
You may prefer to use the Visual Merge feature to make conflict resolution easier. To avoid this situation, your VSS Administrator can disable multiple check outs in your project.