$START DATABASE blocks pclose call

Hello, maybe you have an idea for the following strange problem. I'm maintaining an application written with C and ESQL/C. We're using a very old 2.1 Version of the Developement system (but it works) on PC hardware with SVR4 Unix. Eerything works well. This application has to be installed on a customers machine (a RM 400 with Sinix V5.4.2 and Informix 4.1 Release). Because we hadn't this hardware in our company i had to recompile the sources there. No problems and nearly everything works. What's making problems: There is a part of code which accepts a system command, opens a pipe with popen with this command, read the output, close the pipe (with pclose) and returns the output. This code works during the startup phase of the application until the $START DATABASE command in the code will be issued. Immediately after this command, the pclose call goes into blocking state. Maybe someone here has an idea what's going on and can give me a workaround for the problem. Greetings, Joerg