Symptoms

Getting a "compile failed" error when trying to deploy a process, see: http://screencast.com/t/80WECSULa The process contains steps with custom expressions nested together and are layers deep. The expressions are added to the email body of a "send email" step
 

Diagnoses

The underlying build error is due to the size of all strings in the resulting .NET assembly exceeding 16MB. The exact error in the debug log captured is 'No logical space left to create more user strings.' Also, looking closer at the KOServer.cs file we can see a large string in the email body which is mostly made up of the nested expressions. Essentially, the workflow is this particular case, due to its design structure, was hitting the .NET limitation due to the size of the expressions being used in the design.
 

Resolution

Revise the logic in the expressions to make them a bit more simplified. In this particular case customer was using a large number of logical AND conditions which are nested up to nine levels deep. Alternatively, you can break or move some of the expressions to different sub workflow(s), evaluate the expression in the sub-workflow(s) and then return the result back to the parent workflow.