Im guessing your on shared hosting, and it looks like they have disabled some of PHPs functions. Also its likely that the blank pages are a result of the PHP memory_limit being set to 8Mb. There is a link from InstallTiki with the requirements Tiki needs to run. Ideal would be memory_limit to 16Mb but 12mb should be good. Mines set to 32mb
If you are indeed on shared hosting, you may have no option but to change. TikiFriendlyHosts should be able to guide you there.