The following table shows the general .NET exception classes, in alphabetical order. The description provides common causes of each exception. Use the Object Browser in Visual Studio to explore the following exceptions.

Exception class	Description
AppServerIOException	A general I/O exception was raised while initializing a connection to an OpenEdge application server, and the connection was not completed.
BadURLException	Invalid URL format in connection parameter.
BrokerIOException	A general I/O exception was raised while attempting to initiate a connection to an OpenEdge application server, and the connection was not completed.
BusySessionException	Busy servicing another request.
ConnectAIAException	A connection attempt to an AIA/APSV adapter returned and the connection was not completed.
ConnectException	Error connecting to application server.
ConnectFailedException	Failed application server connection attempt. The message contains the specified reason for the failure.
ConnectHttpAuthException	The HTTP BASIC userid/password authentication failed when connecting to an AIA/APSV adapter, and the connection was not completed.
ConnectHttpsAuthException	The HTTPS (TLS) connection’s authentication failed when connecting to an AIA/APSV adapter, and the connection was not completed.
ConnectProtocolException	An uncategorized error occurred while attempting to initiate and initialize a connection to an OpenEdge application server, and the connection was not completed.
ConnectProxyAuthException	An error was detected while attempting to initiate and initialize a connection to an AIA/APSV adapter via an HTTP proxy server, and the connection was not completed.
DeletedRowAccessException	Application tried to access a deleted row in a SDOResultSet object.
HostUnknownException	Invalid NameServer host specified in the URL.
InvalidNameServerPortException	Invalid NameServer port specified in the URL.
MsgVersionInvalidException	Incorrect version for message received from NameServer.
NameServerClientPortException	A free UDP network port could not be found when attempting to connect to a NameServer and resolve the address of an OpenEdge authentication server, and the connection was not completed.
NameServerClientPortRangeException	The range of UDP port numbers configured for connecting to a NameServer included an invalid value, and no NameServer connection was attempted.
NameServerClientPortRetryException	The number of allowed retries to connect to a NameServer and resolve an OpenEdge application server network address was exceeded, and the connection was not completed.
NameServerCommunicationsException	NameServer communications error. The message contains the specified reason for the failure.
NameServerInterruptException	NameServer communications broken. Either no response was received from the NameServer or the thread was interrupted before the response was received.
NameServerMessageFormatException	Invalid format for message received from NameServer.
NoSuchAppServiceException	Application Service specified is unknown.
NetworkException	A socket I/O error occurred on the connection to the application server.
NoSuchAppServiceException	Application Service specified in URL unknown to NameServer.
Open4GLError	System errors.
Open4GLException	The root exception for all Open Client conditions.
OutputSetException	Output ResultSet error, for example, trying to get a column value out of column order or trying to make an illegal type conversion.
ProDataException	Standard exception for errors that occur while using the ProDataGraph object.
ProException	The base class for all customer-visible Open Client errors.
RunTime4GLAppErrorException	When the top level ABL procedure does RETURN ERROR or throws a Progress.Lang.AppError.
RunTime4GLErrorException	When an ERROR condition is returned from the top level ABL procedure.
RunTime4GLException	Corresponds to ABL ERROR, STOP, and QUIT conditions.
RunTime4GLLockConflictException	This condition is returned from the top level ABL procedure when a lock conflict occurs and the application opted not to wait or when the -lkwtmo has been exceeded.
RunTime4GLQuitException	ABL QUIT condition.
RunTime4GLStopException	ABL STOP condition.
SchemaValidationException	A schema validation inconsistency occurred when using the ProDataGraph object.
SystemErrorException	An unexpected error that indicates an ABL bug or an unusual environmental problem (such as running out of disk space).
UnknownHostnameException	The host address/DNS name specified when connecting to an OpenEdge application server was invalid and the connection was not completed.