Have you installed any updates recently? If so, this may apply.
 
From Lynn's update instructions-
If you are a new IS Tech Subscriber or have not already installed the 12/22/03 or later update, then after installing this update before you can enter any customer payments in AR-C or AR-N or post invoices in SO-G, you will need to run ISARCHK at UT-A to convert to long check numbers. You can also use SM-K or UT-A, program TOOLBAR at each workstation to turn on the IS Tech Toolbar for web and image links. You will see the toolbar icons in the upper right corner of IN-A among other programs, when it is turned on.If you have not already done so, to turn on the Sales Order Change tracking and/or on time delivery reporting, before you can set the default in SD-Q, you will need to get all users out of DBA, load the program using the Classic DBA menu (not Evo), change to the Default (B) company (if you are not already in that company) and go to UT-A, program UPDFILE. Choose the ISARCHG file and click Process to add the new file to the system. If you have Evolution, you then need to download the file and follow the instructions from www.istechsupport.com/datadict.asp.