Error when entering query statements using "@@" functions: "System.AccessViolationException: Atte (4222044)

When using @@ in queries, the following error occurs in Toad Editor window:

System.AccessViolationException: Attempted to read or write protected memory. This is often an indication that other memory is corrupt.

Stack trace:

at QP5Proc16(Int32 , Void* , Int32 , Int32 )
at Quest.QP5.?A0xea684c35.StringQP5Proc(Int32 msg, Void* handle, Int32 lptr1, Int32 lptr2)
at Quest.QP5.Piece.ParseInfo(ParseInfoFlag info)
at Quest.Toad.CodeInsight.BaseDialect.ChunkParseInfoToTokenList(IParsable chunk)
at Quest.Toad.CodeInsight.BaseDialect.GetInsight(IConnection connection, Chunk chunk, Int32 offset, String defaultSchema, Int32& startOffset, Boolean& hasSecondary, Boolean filtering, Boolean secondary)
at Quest.Toad.Editor.Commands.InvokeMemberListCommand.FetchMemberListItems(Object editorText)