Maybe this info might help

If you run Xfire when you crash, Xfire generates an exception report, stating what caused the program to explode. Here's the most frequent report that I get when I crash.

<Application Build="27753" Command="&quot;c:\program files\steam\steamapps\darkgamer\source sdk base\hl2.exe&quot;  -game sourcetest -steam -game &quot;c:\program files\steam\SteamApps\SourceMods\fortressforever&quot; -dxlevel 81"/>
<OperatingSystem Type="2"><Version Major="5" Minor="1" Build="2600"/></OperatingSystem>
<Exception Code="C0000005" Address="0D8FB423"><Module Section="0001" Offset="0000A423" FileName="c:\program files\steam\steamapps\darkgamer\source sdk base\bin\datacache.dll"/></Exception>
<Registers EAX="000005B0" EBX="00000000" ECX="1BA31148" EDX="0752F180" ESI="0D90EA18" EDI="00000090" CS="001B" EIP="0D8FB423" SS="0023" ESP="0012E6A0" EBP="00000001" DS="0023" ES="0023" FS="003B" GS="0000" Flags="00210202"/>

The C++ Error that preceeds this report is the -pure virtual function call error.

Just got a different exception report. So far, all these problems seem to be with the Source SDK Base dlls. I've validated and reinstalled it, so it's how it is supposed to be.

<Application Build="27753" Command="&quot;c:\program files\steam\steamapps\darkgamer\source sdk base\hl2.exe&quot;  -game sourcetest -steam -game &quot;c:\program files\steam\SteamApps\SourceMods\fortressforever&quot; -dxlevel 81"/>
<OperatingSystem Type="2"><Version Major="5" Minor="1" Build="2600"/></OperatingSystem>
<Exception Code="C0000005" Address="143A10CF"><Module Section="0001" Offset="000200CF" FileName="c:\program files\steam\steamapps\darkgamer\source sdk base\bin\serverbrowser.dll"/></Exception>
<Registers EAX="00001FF4" EBX="00001FF4" ECX="0FF55938" EDX="00000000" ESI="00D25278" EDI="14437A38" CS="001B" EIP="143A10CF" SS="0023" ESP="1454EF9C" EBP="00000000" DS="0023" ES="0023" FS="003B" GS="0000" Flags="00010287"/>
<BackTrace>
</BackTrace>