We recently had a customer who after having experienced multiple crashes while running PRTG under Windows Vista 64-Bit updated to version 220.127.116.117 only to notice that PRTG did not even start up properly but was crashing while in the process. Basically, his experience was that upon starting PRTG the "Loading..." screen would show up for a couple of seconds and the program would crash almost immediately, triggering the typical "solution search" window well known to Vista users.
Seeing as we could not emulate the problem at our end, we ended up requesting information concerning the actual machine on which the software was installed, considering we had prior experiences with chips and other hardware peripherals and settigs, as well as other programs having strange effects on the software (see "Negative PING times on AMD Dual Core Processors - Solved
After going through the list of the hardware and software available on the customer's machine we couldn't imagine that anything but some sort of security mechanism was causing the program to crash, as such we suggested turning off Data Execution Prevention (DEP) which, as it turned out, fixed the issue to the customer's satisfaction.
Basically, DEP is a execution protection functionality (both hardware and software based) used to avoid having malware automatically start up, respectively run on the machine with active DEP. In general, it is sound practice (at least for test purposes) to turn off DEP for authorized software showing startup or runtime issues, in order to ensure this is the not the cause for crashes / hangups. In the case of PRTG for the customer mentioned above it sufficed if the DEP scan is turned off for the executable: PRTG Traffic Grapher.exe.
Further information around DEP can be found on the following Microsoft site: http://support.microsoft.com/kb/875352