You can enable debugging logs for all interactions through the SDK by turning on middleware Logging - Basically these log the actions performed by iManage.dll.
The log paths registry key will provide the location of the log. Any application using iManage.dll will spawn a new file based on it's process name (such as YOURAPP.txt, WINWORD.txt, OUTLOOK.txt, etc)
Create or set the following values in HKEY_LOCAL_MACHINE\Software\Interwoven\WorkSite\8.0\Common
Name: Middleware Log Path
Type: String
Value: C:\Temp
Name: Middleware Log Flags
Type: DWORD
Value: ffff
This will show you useful information but the best way to debug is to pare your search parameters right back to basics then slowly introduce more complex parameters. Workspace search requests are made up of both IManage.IManProfileSearchParameters and IManage.IManWorkspaceSearchParameters
and I've found that depending on the data sometimes you'll need to search only with the IManProfileSearchParameters and leave IManWorkspaceSearchParameters as default empty parameters.