Generally speaking, each slip needs to have 2 codes in them, an A code, which is the Activity and an L code which is usually the reference.  Do you have both for every slip?  You don't say what version of Timeslips.  Your Ledes client should have sent you documents of what they need in the export field.  Looking at Timeslips 2014, if you go to Help and type in Ledes you will get some basic instructions there.

I am using Timeslips 2014.

Thank you for your suggestion - I do not see anything with an "L Code" in any of my slips; all I have are "A Codes"... I do not see a place where I would be able to add another task code - How would I go about this?

The "L" (or whichever your client requires) codes need to be typed into a Reference list for a client or template in such a way that they can be used for other matters without having to retype the list each time. This can take some time to set up and test, and can be daunting the first time you do it. If you want to tackle it yourself, you should be able to get there using the spec document from your client (request it if you don't have it) and the Timeslips online Help. If you would like assistance, any number of us Certified Consultants on this group would be able to help you privately. We have all done this many times.