Hello. I am running a DNN4 installation that has operated great for years. 

Error displays in events as as follows, any suggestions are really appreciated. Im interested in advanced developers that I could retain services from to assist in sorting this out

Several pages on the site just hang when they are being accessed now. In IIS the worker process seems to climb until the app pool resets.  

PortalID: -1
PortalName: 
UserID: -1
UserName: 
ActiveTabID: -1
ActiveTabName: 
RawURL: 
AbsoluteURL: 
AbsoluteURLReferrer: 
UserAgent: 
DefaultDataProvider: 
ExceptionGUID: 
InnerException: ASSIGNING SourceTabInfo = 261 = 261DisplayListTabInfo = 261 = 261DisplayTabInfo = 261 = 261
FileName: 
FileLineNumber: -1
FileColumnNumber: -1
Method: 
StackTrace: 
Message: System.Exception: ASSIGNING SourceTabInfo = 261 = 261DisplayListTabInfo = 261 = 261DisplayTabInfo = 261 = 261