RE: Error Code 1602 & SP1
This isn't nessecarily related to the SP. It's more likely that you hsve an over abundance of layer filters built up from legacy drawings. The lisp routine at the end of the thread for Layer Manager & Layer drop down are slow to open in the AutoCAD FAQ Forum should solve your issues.
RE: Error Code 1602 & SP1
Deleting the Layer Filters did the trick. Also, there were a large number of Registered Apps attached to the file. After purging those out, the files are working fine.
Thanks for your help.