Automating Visual Studio with EnvDTE

As a solution to this issue you can register to an event that notifies when the solution load is done.

This is a sample of class that lets you listen to events on solution loading:

public class SolutionEventsListener : IVsSolutionEvents, IDisposable
{
    private IVsSolution solution;
    private uint solutionEventsCookie;

    public event Action AfterSolutionLoaded;
    public event Action BeforeSolutionClosed;

    public SolutionEventsListener(IServiceProvider serviceProvider)
    {
        InitNullEvents();

        solution = serviceProvider.GetService(typeof (SVsSolution)) as IVsSolution;
        if (solution != null)
        {
            solution.AdviseSolutionEvents(this, out solutionEventsCookie);
        }
    }

    private void InitNullEvents()
    {
        AfterSolutionLoaded += () => { };
        BeforeSolutionClosed += () => { };
    }

    #region IVsSolutionEvents Members

    int IVsSolutionEvents.OnAfterCloseSolution(object pUnkReserved)
    {
        return VSConstants.S_OK;
    }

    int IVsSolutionEvents.OnAfterLoadProject(IVsHierarchy pStubHierarchy, IVsHierarchy pRealHierarchy)
    {
        return VSConstants.S_OK;
    }

    int IVsSolutionEvents.OnAfterOpenProject(IVsHierarchy pHierarchy, int fAdded)
    {
        return VSConstants.S_OK;
    }

    int IVsSolutionEvents.OnAfterOpenSolution(object pUnkReserved, int fNewSolution)
    {
        AfterSolutionLoaded();
        return VSConstants.S_OK;
    }

    int IVsSolutionEvents.OnBeforeCloseProject(IVsHierarchy pHierarchy, int fRemoved)
    {
        return VSConstants.S_OK;
    }

    int IVsSolutionEvents.OnBeforeCloseSolution(object pUnkReserved)
    {
        BeforeSolutionClosed();
        return VSConstants.S_OK;
    }

    int IVsSolutionEvents.OnBeforeUnloadProject(IVsHierarchy pRealHierarchy, IVsHierarchy pStubHierarchy)
    {
        return VSConstants.S_OK;
    }

    int IVsSolutionEvents.OnQueryCloseProject(IVsHierarchy pHierarchy, int fRemoving, ref int pfCancel)
    {
        return VSConstants.S_OK;
    }

    int IVsSolutionEvents.OnQueryCloseSolution(object pUnkReserved, ref int pfCancel)
    {
        return VSConstants.S_OK;
    }

    int IVsSolutionEvents.OnQueryUnloadProject(IVsHierarchy pRealHierarchy, ref int pfCancel)
    {
        return VSConstants.S_OK;
    }

    #endregion

    #region IDisposable Members

    public void Dispose()
    {
        if (solution != null && solutionEventsCookie != 0)
        {
            GC.SuppressFinalize(this);
            solution.UnadviseSolutionEvents(solutionEventsCookie);
            AfterSolutionLoaded = null;
            BeforeSolutionClosed = null;
            solutionEventsCookie = 0;
            solution = null;
        }
    }

    #endregion
}

Usage example:

DTE2 applicationObject = dte;
var serviceProvider = new ServiceProvider(applicationObject as IServiceProvider);
solutionEventsListener = new SolutionEventsListener(serviceProvider);
solutionEventsListener.AfterSolutionLoaded += () => /* logic here */ ;