Editing an enterprise custom field lookup table, I received an unexpected error with no other information in the PWA page.  The following error appeared in the ULS log.

Application error when access
/_vti_bin/PSI/LookupTable.asmx, Error='gzip' is not a supported encoding
name.  Parameter name: name 

 at System.Globalization.EncodingTable.internalGetCodePageFromName(String

 at System.Globalization.EncodingTable.GetCodePageFromName(String

 at System.Text.Encoding.GetEncoding(String

 at Microsoft.Office.Project.Server.PSIForwarderHandler.ProcessRequest(HttpContext

 at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()   

 at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean&

I clicked on Start > Administrative Tools and launched Internet Information Services (IIS) Manager.

I clicked the root node of the server.

Then, I double-clicked Compression.

I unchecked "Enable dynamic content compression" and clicked Apply.

I reset IIS from a command prompt using the command iisreset.

I was then able to open the custom field lookup table successfully without error.