We have been successfully running 6.5 for many months.  This weekend, we upgraded to TC 7.
After it was all upgraded and the server restart, without making any code changes, we just pressed the Run button on an existing build.  Instead of the normal 5 minute build length, the build took 48 minutes.   This time was consistent the next three times we ran the build.
Looking at the build logs, it looks like there is some step just before our nUnit tests are run that takes 42 minutes whereas it previously took 7 seconds.   Please see the build log exceprts below.

How can we debug, fix, or improve this situation?
Thanks.

[15:57:56]Step 2/6: nUnit Tests (NUnit) (45m:12s)

[15:57:56][Step 2/6] Starting: "C:\Program Files (x86)\TeamCity\buildAgent\plugins\dotnetPlugin\bin\JetBrains.BuildServer.NUnitLauncher.exe" #TeamCityImplicit

[15:57:56][Step 2/6] in directory: C:\Program Files (x86)\TeamCity\buildAgent\work\af9961a4bc4ce9dd

Previously with 6.5, this was the log:
[22:59:51]Step 2/6: nUnit Tests (NUnit) (2m:52s)

[22:59:51][Step 2/6] Starting: "C:\Program Files (x86)\TeamCity\buildAgent\plugins\dotnetPlugin\bin\JetBrains.BuildServer.NUnitLauncher.exe" #TeamCityImplicit

[22:59:51][Step 2/6] in directory: C:\Program Files (x86)\TeamCity\buildAgent\work\af9961a4bc4ce9dd