It would be very painful to debugg the workflow, VS provides help to some extend, however for details log information you have to change the web.config for your web application in which the workflow is running under.

 

 

Open your web.config,

Add the below nodes,

...................................

<system.diagnostics>
<switches>
<add name="System.Workflow LogToFile" value="1" />
<add name="System.Workflow.Runtime" value="All" />
<add name="System.Workflow.Runtime.Hosting" value="All" />
<add name="System.Workflow.Runtime.Tracking" value="All" />
<add name="System.Workflow.Activities" value="All" />
<add name="System.Workflow.Activities.Rules" value="All" />
</switches>
</system.diagnostics>
</configuration>

The log file created under C:\WINNT\system32\inetsrv 

MSDN Article http://msdn2.microsoft.com/en-us/library/ms732240.aspx