I have main report with subreports. The subreports have common fields with the main report.  Links have been made on those common fields.  Share string variables have been created and information can be passed to the main report from the subreports.  However,  there is one field that is not common between the main report and subreport.  This field is common between the subreports. How can I accurately pass this field in a variable to the main report?

you will have to create a shared variable in the subreport and then pass it to the main report and from the main report then pass it to the second subreport.just make sure that the subreport where you will create the variable should be in a different section then the subreport you need to pass the data too.I have actuatlly done this is my reports and it works fine!.This is how we link two subreports and create nesting

You need to link the main report with the second subreport with that shared variable.

how are you linking the subreport to you main reports are you passing the variable in the query as a parameter.also  please place the initiating variable in some section of the first subreport .u can suprees it.