I've run into Monarch's brick wall, otherwise known as the maximum number of fields, a few times. It's usually because I've tried to create too many summaries in one model (yes, that affects the number of fields in use in the model).
The solution in those cases is to duplicate the model as is (save the current model, then save it again under a new name), and then delete the existing summaries and get on with building replacements. In this way you can build as many summaries as you need. It's unlimited really.
Then you run a little batch file to execute two or more models/projects as required for your end needs.
If summaries aren't in play, though, and it's truly just the Table window that's exceeding the maximum, then you've really only got a couple of options.
I'm not a Data Pump user, but since its foundation is Monarch, and Monarch models, I'd expect that particular technical limitation to be consistent between Monarch and its big brother Data Pump.
If you're using calculated fields, especially calculated fields that rely on other calculated fields, then you can consolidate them by integrating the formulas as necessary.
Worst case scenario is that you're really trying to capture 255 individual fields from a report, which would be quite rare, IMO, and argueably is not a good design and propbably not something that should done, to be honest. Proper normalization techniques will build a more useable data set, even if the model is built purely for analysis purposes.
Capturing smaller collections of fields and grouping them in a logically related manner, along with a common key, would be best exported to a format like an Access database file, where each collection of related fields becomes its own table.
Just to add a couple of pointers - if you're working from a report file then you might be dealing with very long lines to have so many fields. You can use Monarch Utility to prepare data (forcing new line after n characters), and then you might be able to use Monarch's multi-line fields, and memo fields, to extract the data more efficiently.
Another common problem is when each record contains multiple values, such as stock prices for every day of the year. You can't have 365 fields but you can get hold of the data using Monarch's multiple column region feature. This only handles 40 columns in Monarch v10, but multiple passes can be used to overcome this.
If you post a sample report or can email something, I'd happily have a look to make some practical suggestions.
The file has sensitive data, so I cannot post a sample of it. It is a fixed width file that has about 150 fields in it. I have to make some additional fields that are calculations off of existing fields and that is bringing me over the 255 limit.
What I did for now, is break it into 2 databases and merged them with MS Access.