A VPWL_F_RE_FOREVER part is a for a VPWL_FILE that repeats forever. The first thing to check is that the file works as a VPWL_FILE and then work on the repeating. The "file" for a VPWL_FILE part is a tab delimited text file with two columns, time and value, the "time" must be monotomic (increasing), and both values can take any legal PSpice notation for value, including scientific or multiplier, 0,0 is assumed as the start if a 0 time value is not specified, linesr interpolation is used between the specified points inthe file. The "FILE" property of the part in the schematic takes the FULL PATH and FILE NAME for the referenced text file. (As in C:\MyDir\MyFile.txt)
STL files created with the Stimulus editor are not valid sources for the VPWL_FILE parts, they are used with the VSTIM parts for voltage. (There are ISTIM parts for current sources) The PSpice Reference Manual describes Independent Voltage (and Current) Sources.