We’re using Oracle EBS release 12 for our business and we are stuck with Oracle Developer 10g as we have many inhouse developed applications, especially for Order Management requiring frequent development and maintenance.
Once in a while, after Windows updates, Oracle’s obsolete development suite starts acting weird (Windows wouldn’t maximize, sporadic internal errors…) & ironically, restarting fixes most of them.
Recently, I had some issues with Report developer 10g. The error message was “internal error [ph2exp:case]”. As an “experienced” PL/SQL developer, I was sure that my code was great and these errors WERE another set of issues produced by Oracle’s obsolete stack. Well, I was wrong.

The error was due to constructing the operators wrongly. Instead of “Greater than or equal to” I set up “Equal to or greater than” causing the compiler to raise the error. Oracle document 1093084.1 should give you more information.
Hence, if you ever run into this compiler error, please don’t blame Oracle. Just correct the positions of the operators.